Car number plates, once they have outlived their legal use as unique identifiers of cars, often become collectible items. This hobby is known as car number plate, or vintage number plate, collecting. Car number plates generally date back to the early twentieth century; in the UK, the 1903 Motor Act introduced car registration as a legal requirement. There are some older examples in other countries, which, of course, are highly valued as collector items because of their age.

Other car number plates can be valued as collector items due to their colour, regional origin, shape and / or size and historical peculiarities. Particular combinations of numbers and / or letters can be valued for their rarity or special value. Personalised car number plates, also known as vanity or cherished number plates, are among the most highly valued and collectible.  These can be very expensive and are usually registered index marks displayed on a vehicle being used.  In all cases however, unless national licensing authorities have given specific legal consent, collected car number plates cannot be displayed on a vehicle being driven on a public road.

Collectible car number plates are often offered at auctions. Other collectors browse through old junk sales, garage sales, car scrap yards, and so on, hunting for these collectors’ items. In some countries, specific collectors’ associations have been set up, such as the Automobile Licence Plate Collectors Association (ALPCA) in the US. In recent years, the number of website and social media sites devoted to collecting private number plates has grown greatly in number.