I bought a car about a month ago, when I moved to Northern California. It was not new, having been used by the dealer as a demo car. It had license plates, but the tax had expired. The dealer gave me a temporary permit and told me that the DMV would send me the tax stickers and the pink slip in six-eight weeks.
The pink slip is the government issued document that demonstrates your ownership of the car. Unlike the famous green card, which is not green; the pink slip is actually coloured pink. Rather that have a sticker for the windscreen, the US tax stickers adhere directly to the license plate.
The package arrived from the DMV today, a day over the six weeks. As well as the expected pink slip and tax stickers, they supplied two new license plates. In the UK, a car has the same plates from registration until it is scrapped and they are used as the primary identification for the car. The arrival of these new plates was, therefore, a surprise. In the UK, a change of plates would require contacting my insurance company, but here the 17 character VIN (Vehicle Identification Number) is used as the identification code. If changes in ownership cause changes in license plate numbers, I can see why the VIN is used. It also has the advantage of confirming the details of the car, as the VIN can be decoded to tell you the make, model, and year of manufacturer (In fact, you can even tell the assembly plant in which the car was built)