I painted my 1950 Utah plates (Black and Orange) using appliance enamel sold by Rustoleum. This is a very tough paint and worked really well. My numbers were in decent shape so I just painted the black background. If you mask the numbers using striping tape it won't pull the paint usually. I also use toothpicks and as soon as I shoot around the number I pulled the tape and smoothed all the transitions with the toothpick so it doesen't look sprayed at all. If you paint both the numbers and the background I would do 1 number or letter at a time. I have some pics of this work I also did it with my hubcaps with the small Chevrolet letters on them, and an old Coke Machine.
