here in the UK a vehicle registration number is issued to a vehicle, the number plate could then be made up by anyone using a variety of methods, but in recent years to prevent criminal activity they should be made by only reputable dealers after you give various items of proof of ownership, but you can still get them made up as show plates by other people in various sizes shapes and any font style. This is just a very simplistic description of what over the years has been a complicated system. I believe in the US you go to your state registration department and are issued with the next available plate which stays with you for life.