Airmail etiquette
An airmail etiquette, often shortened to just etiquette, is a label used to indicate that a letter is to be sent by airmail. The term is from French "étiquette" "label, sticker" (cognate to "stick"), from which also comes the English word etiquette "rules of behavior". Use. Because the etiquettes are just instructions to postal clerks, and have no monetary value, their printing and distribution need not be as carefully controlled as for postage stamps, and most are privately produced. The usual design is a plain blue oblong, with the phrases "AIR MAIL" and/or "PAR AVION" in white letters . Airlines and hotels have also produced etiquettes, some quite attractive. The airmail etiquette may be omitted if airmail stamps are used on the letter, and in some cases even this is not necessary if a country sends out all its foreign mail by air. In some countries, such as the United Kingdom, one may simply write "PAR AVION -- BY AIR MAIL" on the envelope, even though etiquettes are available free from post offices. The United States officially requires international First Class and Priority Mail letters to be marked with "AIRMAIL/PAR AVION". This requirement is often ignored in modern practice  since the USPS discontinued surface mail in 2007; all international mail from the US is now sent via airmail. Pre-printed airmail etiquettes are no longer produced by the US Post Office.