[lkchris]

Well, when your state motor vehicle department issues you a license plate it's only valid for one vehicle ... you can't use it on multiple vehicles or any vehicle you want. They make this association using your vehicle identification number. Your question is about the same as asking why you need a number on your house or apartment.

In addition there are Federal laws enabling the government to require a vehicle be recalled to fix an emissions or safety problem ... manufacturers identify applicable vehicles via VIN. And they find your address (and your house number) to send you a recall notification letter by associating your address with your registration by VIN.