Title: Vehicle registration plates of Portugal
Content:  In March 1992, the AA-00-00 format came to an end and was succeeded by the genuinely national-level 00-00-AA sequence. The type of plate also changed to black characters on a reflective white background, with the blue ribbon, with the emblem of the European Communities (now Union) on the left hand side and the letter P as a country identifier. Under this new sequence no combination of letters was reserved for specific entities or areas. However, in 1997 the combinations KA to KZ, the first letter of which sequence does not occur in the Portuguese alphabet and so had not previously been used, were given over to preregistered imported vehicles. The groups WA 
Title: Vehicle registration plates of Argentina
Content:  In October 2014 the design of the new license plate to be used by all Mercosur countries was officially presented. It consists of a plate of 400 x, with a white background, the characters and frame in black and a blue band at the top that shows the name of the country, its flag and the Mercosur logo. The typeface used is FE-Schrift. In Argentina, the serial format is AA 000 AA, allowing a total of 450 million combinations. The system started with AA 000 AA, AA 000 AB ... AA 000 AZ, AA 000 BA... AA 000 ZZ, AA 001 AA... By January 2017, there were plates with license numbers as high as AA 950 AA. It is expected the AB series to start in February 2017. Series AC started in December 2017, while AD started in November 2018. As of April 2019, the highest number is AD530.
Title: Vehicle registration plates of Italy
Content:  Agricultural machines have motorcycle-sized plates following the AA-0/00A scheme written in black on yellow. Agricultural trailers have the text "RIM AGR." in red on the upper part. The style is same as the old trailer plates but background is yellow and the serial is AA-000A. Agricultural trailers have to show both their own plates and a prime mover repetition one. Agricultural plates from 1994 Agricultural trailer plates from 1994 Agricultural trailer plates from 1985 to 1994 Agricultural trailer plates from 1959 to 1985 Agricultural plates from 1948 to 1985 Agricultural plates from 1985 to 1994 Repeater plate used from 1985 to 1994 Repeater plate from 1994
Title: Vehicle registration plates of New South Wales
Content: Cars and Heavy Vehicles: aa·nn·aa – commenced July 2004. ; Slimline light vehicle series: aaa·nna – commenced 1991. ; Trailers: Ta·nn·aa – commenced December 2014 from TA-00-AA. ; Trailers: Ta·nn·aa – commenced August 2014 from TR-00-AA. ; Motorcycles: aaa·nn – commenced August 1989 from ZZZ-99; progresses backwards (currently issuing 'J' series). ; Motorcycles: aaa·nn – commenced November 2009 from ABA-00; progresses forwards (currently issuing 'F' series). 
Title: Vehicle registration plates of Estonia
Content: A1 - Plates for general use on cars and trailers (vehicle categories M, N and O). ; A2 - Special-order plate. Must contain at least one letter and one number up to a total of 9 characters. Numbers and letters may not alternate. ; A3 - Plates for general use with reduced size. Usually used on cars with American origin, contains two numbers and three letters (historically beginning with Z). ; A4, A5 - General diplomatic plates with white letters on a blue background. A4 plates consist of two letters (usually CD) and four numbers, A5 are restricted to heads of diplomatic 
Title: Vehicle registration plates of the Philippines
Content: "AAA, AAH, AAI, AAJ, AAK, AAL, AAM, AAN, AAO, AAP, AAQ, AAW, AAX, AAY, AAZ, ABA, ACA, ADA, AEA, AFA, AGA, AHA, AIA, AJA, AKA, ALA, AOA, APA, AQA, ARA, ASA, ATA, AVA, ABB, ABC, ABD, ABE, ABF, ABG, ABH, ABO, ABP, ABQ, ABR, ABS, ABT" – National Capital Region ; "AAA-ABV; ABA-ATA, AVA-AXA"– Public Utility Vehicles (All regions with indicating the type of service, ex. tourist vehicles from 2014 to 2016) ; "AUA, BUA" – NCR, Region I, Region II, Region III, Region IV-A, Region XI and Region XII – Public Utility Trailer (2014–2016) ; "AUA, BUA" – NCR, Region II, Region III, Region IV-A, Region VII and Region XII – Trailer (2014–2016) 
Title: Non-passenger and optional vehicle registration plates of Georgia (U.S. state)
Content:  The state streamlined the ever-growing number of limited-issuance plates by instituting two-letter prefixes for almost all types other than standard passenger plates. For most types, the serial format progresses after the two-letter prefixes in the following sequence: 0, 00, 000, 0000, 000A, 00A0, 0A00, 00AA, 0AAA, and 0AA0. Many of these plate types first appeared on the www.GEORGIA.gov base in December 2003 or later, but beginning in the first quarter of 2007, some types began transitioning to the GEORGIA.gov base, with nearly all types having made the transition by the first quarter of 2008. On the new base, the county sticker box and remaining (right) year sticker box were removed.
Title: United States license plate designs and serial formats
Content:  License plate numbers are usually assigned in ascending order, beginning with a starting point such as AAA-001. Thus, an observer familiar with the sequence can determine roughly when the plate was issued. In a few cases, numbers have been assigned in descending order. For example, when Virginia switched to seven characters for its standard issue in 1993, numbers beginning with AAA-1000 were already in use for extra-cost, optional-issue plates; therefore, the new standard license plates were issued in descending order from ZZZ-9999.
Title: Vehicle registration plates of South Australia
Content:   Vehicles and trailers: S000·ABC  Motorcycles: S00·ABC In South Australia, until October 2008, standard registration plates followed the 3-letter, 3-number (aaa-nnn) standard used by New South Wales and Victoria: their series, introduced in 1966 started with RAA-000 and finished at XUN-299. Since October 2008, South Australian general issue plates follow the format Snnn-aaa, the S signifying South Australia. No slogan is printed on these plates, rather they contain the words 'South Australia'. Up until 1966 South Australian plates were all numerical, and were subject to re-issue, in either nn-nnn or nnn-nnn format, white on black background. These plates are available for re-issue at a fee. Post 1966 motorcycles were initially issued with RA-000 to SZ-999 then TAA-000 to TIZ-999. Trailers were issued TJA-000 to TZZ-999. When the Taa-nnn issues were exhausted, motorcycles were issued with high end YYA-000 to YZZ-999, then started at YKA-000 to YKA-799, and trailers issued YAA-000 to YIL-999. Since 2008, newly issued plates are in the form S000-AAA and motorcycles as S00-AAA, while trailers start at S000-TAA.
Title: Vehicle registration plates of Massachusetts
Content:  Massachusetts also issues "reserve" plates. Reserve plates permit the plate holder to receive the same serial number when new plate styles are issued, or to transfer the serial number to family members. These plates are either all-numeric (1 through 99999) or consist of a single letter followed or preceded by a number (A 1 through Z 9999 and 1 A through 9999 Z). Reserve serials may also be of the forms A#A, A##A, #A#, and #AA#, where # represents any number, and A represents any letter. Low-number reserve plates – now called "Lottery Plates" by the RMV – are of the forms #, ##, ###, ####, A#, A##, #A, and 

Question: what does aa on a license plate mean?
Answer: cars of the royal family.