A license plate or number plate is a small metal plate attached to a vehicle. The plate has a serial number on it which uniquely identifies the vehicle.
In Canada, Mexico, Australia, and the United States, license plates are issued by provinicial/territorial/state governments. Their appearance is frequently chosen to contain symbols, colours, or slogans associated with the issuing state. The license plate number's format is chosen to provide enough numbers for all the motor vehicles in the state: Wyoming, the smallest U.S. state by population, uses NN NNNN or NN NNNL, with the first two numbers restricted to 1-23 and 99; Rhode Island, the smallest state by area, uses the formats LLNNN and NNNNN; while California and other populous states use NLLLNNN, where N is a number and L is a letter. Plates on trucks may have different formats such as NLNNNNN.
People can pay extra and get vanity plates: license plates with custom messages on them. Vanity plates are not allowed to have profane or obscene messages on them, and of course they must also be unique. In some jurisdictions, including virtually all U.S. states, vehicle owners may also pay extra for speciality plates: with these, the sequence of letters and numbers is chosen by the licensing agency--as with regular plates--but the owners have a broad choice of plate designs.
The allocation of codes in maintained by the United Nations as the Distinguishing Signs of Vehicles in International Traffic, being authorized by the UN's 1949 and 1968 Conventions on Road Traffic. Many, but far from all, vehicle codes created since the adoption of ISO 3166 coincide with either the ISO two or three letter codes.
For a full list of license plate country codes, see List of international license plate codes.International codes
On the international level the license plates of different countries are distinguished by a supplementary license plate country code. This country designator is displayed in bold block uppercase on a small white oval plate or sticker on the rear of the vehicle near the number plate.
