It’s “Driver’s License” in my state (Idaho), while it’s a “Driver License” in California. I always assumed that the possessive form was to indicate that it was

It’s “Driver’s License” in my state (Idaho), while it’s a “Driver License” in California. I always assumed that the possessive form was to indicate that it was a license possessed by a driver. In fact “Driver License” makes less sense in my head, as I can’t make heads or tails of what role each word is supposed to make in that clause.