Car tags, also known as vehicle registration plates, are legally required vehicle identifiers that show proof of registration, insurance, and ownership. They are issued by a government authority and are only valid for one year at a time. While almost all motor vehicles are uniquely identified by a vehicle identification number, only registered vehicles display a vehicle registration plate and carry a vehicle registration certificate. In the United States, each state has its own system for issuing car tags, and the requirements for obtaining them may vary. In Florida, for example, a registration certificate must be in the possession of the operator of the motor vehicle or carried in the vehicle at all times. The registration certificate often also acts as proof of ownership, though technically this is not the case. Ownership of the vehicle may be checked through the Personal Property Securities Register of the federal government, though this is not a mandatory register. Car tags must be renewed annually, with the payment of a fee.