Source: https://crwflags.com/fotw/flags/int-red.html
Timestamp: 2019-04-26 00:44:30+00:00

Document:
The precise appearance of these flags is not prescribed. The versions shown above are in use, the last three being exported from .eps files on the ICRC web site.
Kindersley (1997) states (in the Tonga page) that the flag with the red cross coupee was adopted in 1863.
Geneva I, Art. 38, provides for use of the Swiss federal arms in reversed colors, the red cross on a white ground, as the emblem and distinctive sign of the Medical Service of armed forces. [This was originally provided for in article VII of the first Geneva Convention for the Amelioration of the Wounded in Armies in the Field, signed on August 22, 1864.] The red crescent or red lion and sun, in lieu of the red cross, will be recognized for use by countries that were already using those devices when the 1949 convention was adopted.
Geneva I, Art. 39, requires the emblem (red cross, etc.) to be displayed on the flags, armlets and on all equipment employed in the Medical Service. The same provision is also contained in Geneva II, Art. 41.
Geneva I, Art. 42, limits the display of "the distinctive flag of the Convention" to medical units and establishments entitled to be respected under the Convention and permits it to be displayed in conjunction with the national flag of the party to which the unit or establishment belongs. [The 1864 convention required it to be displayed with the national flag.] When medical units fall into the hands of the enemy, they display only the flag of the Convention.
Geneva I, Art. 43, requires medical units of neutral countries "which may have been authorized to lend their services to a belligerent" to fly the flag of the Convention and the national flag of the belligerent to which they have been lent, and permits them to fly their own national flag as well. Such neutral medical units may continue to fly their own national flags even if they are captured.
Geneva I, Art. 44, bans all uses of the Red Cross or equivalent emblems (including flags) other than to indicate or protect medical units and establishments and related personnel and material under the Geneva Conventions, except that national Red Cross/Red Crescent Societies may use the emblems in peacetime for other activities in conformity with the principles of the Red Cross movement. In wartime, they may use the emblems for their other activities only if they are clearly not implying the protection of the convention. International Red Cross organizations (such as the International Committee of the Red Cross) may use the Red Cross emblem at all times.
Geneva II, Art 43 requires hospital ships to "make themselves known by hoisting their national flag and further, if they belong to a neutral state, the flag of the Party to the conflict whose direction they have accepted. A white flag with a red cross shall be flown at the mainmast as high as possible." Hospital ships that are provisionally detained by the enemy haul down their national colors. Coastal lifeboats operating from a base occupied by the enemy may continue to fly their own national colours along with the Red Cross flag.
Geneva II, Art 44, limits the use of the distinguishing signs, including the flag, to indicating ships and vessels protected by the convention, whether in peace or war (except as otherwise agreed, e.g., by Geneva I).
The main authority to use the red cross/red crescent symbol is not by any international red cross organization (ICRC or IFRC) or national red cross society but by the parties to the Geneva conventions (or any party to a conflict, since the protocol includes civil wars within its ambit) to designate military medical facilities and units. In fact, in both wartime and peacetime the national red cross societies can use the symbol only with the approval of their governments. The same applies to the other symbols provided for under the conventions and the protocol: decisions on where to display them is the responsibility of the authorities of the governments who signed the convention or of the parties to a conflict.
Article 5: "Design of the emblem"
The emblem used as a protective device shall always retain its original form, i.e. nothing shall be added either to the cross, the crescent or the white ground. A cross formed with two cross-pieces, one vertical and the other horizontal crossing in the middle, shall be used. The shape and direction of the crescent are not regulated. Neither the cross nor the crescent shall touch the edges of the flag or the shield. The shade of the red is not specified. The ground shall always be white.
Article 7: "Internal regulations of the National Society"
So, the direction of the crescent doesn't matter -- all versions are valid and "protective". But national societies can decide for one version for "indicative" use (i.e. for consistency of the "logo" within the national society). This has no effect on the protective use, and is optional.
The red cross and the red crescent flags are not formalized to the construction details - no ratio, no explanation how exactly the cross and the crescent should look like, how bold they should be, etc. The intention is not to formalize it, so that any reasonable depiction would be enough to provide protection according to the agreements and international law - i.e., to prevent someone from saying maliciously that the proportions were not "as specified", so they did not have to respect the significance of the symbol. Therefore, the RC flags are made and used in different ratios, 1:1, 2:3, 1:2 all being quite usual. In practice the RC flag tends to be of equal ratio as the flag of the country where it is displayed, but there is no such requirement.
The plain Red Cross or Red Crescent flag is primarily used to identify medical units of military forces as provided by the 1864 and subsequent Geneva conventions, although national governments may authorize Red Cross or Red Crescent societies to use the flags provided there is no possibility of confusion with the primary use of the flag. The convention also allows the various international Red Cross organizations (ICRC and IFRC) to use the symbols. Therefore, the plain Red Cross is not a unique identifier of the ICRC.
The basic right to use the Red Cross and Red Crescent flags does not derive from either of these organizations. It is an inherent right of all states that are parties to the Geneva Convention of 1949 and any other belligerent that might be engaged in combat in accordance with the laws of armed conflict.
"C'est de propos délibéré que l'on n'a pas voulu fixer la forme de la croix rouge, ce qui eut ouvert la porte � des abus dangereux... Si la forme de la croix avait été fixée de façon immuable, n'aurait-on pas cherché � justifier des attaques contre les bâtiments protégés par la convention en prétextant que les signes n'avaient pas les proportions prescrites?..."
Nowadays it is normal that the Red Cross symbol in ordered (i.e. peaceful) conditions is modeled after the Swiss flag, more or less. However, looking at old documentaries it seems to me that before, say 1950's, the shape of the cross was usually much thinner (even to one third of the width of the Swiss cross).
This version of the red cross matches the form of the Swiss national flag.
The Red Crescent flag is used in Islamic nations.
The Red Crescent, the Muslim version of the Red Cross, is depicted as having the upper and lower tips of the crescent to the viewers left. In French Naval Commander du Payrat's publication "Album des Pavillons Nationaux et des Marques Distinctives" the tips of the crescent are to the viewer's right. I observed news photos from Iraq on more than one occasion showing what appear the be field ambulances with the Red Crescent displayed on the side of the vehicle and the crescent's tips are to the viewer's right.
I believe that this is not strictly regulated by the ICRC, just as in the cross emblem version where width and length of the crossbars is irrelevant. It was intentionally left unspecified so that in combat no side might "make mistakes" supported by slight (or big) deviations from a "perfect" pattern.
In 1980 the Islamic Republic of Iran decided to give up the red lion and sun and use the red crescent in its place. This flag is therefore obsolete.
Pedersen (1970) shows a 2:3 white flag with a red cross and crescent (pointing towards hoist). Label is "Russian Red Cross" and caption: "Because of the Moslems among the peoples of the Soviet Union, the Soviet Red Cross combines both symbols in its flag." Proper label would of course better be "Soviet Red Cross and Crescent".
Since Kazakhstan has large numbers of both Christians and Muslims, their society is called "Red Cross and Red Crescent." I believe they are unique- and since the "rules" are that only a cross *or* a crescent may be used, the society has not been recognized. Ironically, this means that the flag of the Kazakhstan society would be the same as (or close to) that of the IFRC itself.
Looking at Victor Lomantsov's Vexillographia site (issue on the CD that he courteously provided to me in Stockholm) I read about the Kazakh Red Cross and Red Crescent society flag. That seems to employ the new symbol consisting of a "red chevron" with the red cross and the red crescent in base of it. As my Russian is not that good (and I have no patience reading it really carefully) I am not sure if that is still a proposal, or if this new symbols is already being used.
Some years ago I have been reading about this new symbol being discussed by the ICRC, but as far as I was aware, the proposal was not yet formally adopted. Are there any changes about that?
From memory, the red chevron symbol was proposed to replace the religious symbols and would therefore remove the unwanted connotations and problems that other religions see in the two internationally adopted symbols (three actually, the third is the red lion-and-sun symbol not used any more). This would enable inclusion of the Red Magen David society too, and would enable the other religions to find their place in the scheme. The world-wide symbol is to be the chevron only consisting of a 45 degrees rotated square that is "missing" the lower quarter. In this quarter the local symbol may be added at will (or after certain regulations) just as the Kazakh flag shows.
The ICRC website is still citing the proposed status of the emblem. As they note, the emblem must first be recognized by the signatories to the Geneva Convention as a symbol of the ICRC. World events appear to have delayed this from becoming an official symbol to date.
Postcard collection shows shipping flag entitled "Red Cross Line" and a 2:3 flag otherwise identical the regular Red Cross.
You can see the flag of the new national society of the Red Cross of Southern Sudan on <http://www.redcross.int/EN/mag/magazine2011_3/in_brief.html>.
In the website of the Afghan Red Crescent Society, you can see the emblem of the Society, the explanation of the symbol, and you can see the flag of this Society in several images of the "Image Gallery".

References: Art. 38
 Art. 39
 Art. 41
 Art. 42
 Art. 43
 Art. 44
 Art 43
 Art 44