International vehicle registration code
The country in which a motor vehicle's vehicle registration plate was issued may be indicated by an international licence plate country code, formerly known as an International Registration Letter or International Circulation Mark. It is referred to as the Distinguishing sign of the State of registration in the Geneva Convention on Road Traffic of 1949 and the Vienna Convention on Road Traffic of 1968.
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The allocation of codes is maintained by the United Nations Economic Commission for Europe as the Distinguishing Signs Used on Vehicles in International Traffic (sometimes abbreviated to DSIT), authorised by the UN's Geneva Convention on Road Traffic and the Vienna Convention on Road Traffic. Many vehicle codes created since the adoption of ISO 3166 coincide with ISO two- or three-letter codes. The 2004 South-East Asian Agreement ... for the Facilitation of Cross-Border Transport of Goods and People uses a mixture of ISO and DSIT codes: Myanmar uses MYA, China CHN, and Cambodia KH (ISO codes), Thailand uses T (DSIT code), Laos LAO, and Vietnam VN (coincident ISO and DSIT codes).
The Geneva Convention on Road Traffic entered into force on 26 March 1952. One of the main benefits of the convention for motorists is the obligation on signatory countries to recognize the legality of vehicles from other signatory countries. When driving in other signatory countries, the distinguishing sign of the country of registration must be displayed on the rear of the vehicle. This sign must be placed separately from the registration plate and may not be incorporated into the vehicle registration plate.