JayDee
FYI: Most spray paint is pretty wimpy stuff, especially compared to original paint surfaces. If one gets a good pair of rubber gloves, a can of lacquer thinner, and a sacrificial old towel, it is easy to remove. Lacquer thinner is highly volatile, and if you pour some on a towel, then quickly rub at the graffiti, it will transfer to the towel. Keep repeating with a fresher part of the towel and fresh solvent, and voila! the graffiti is gone. Just keep the rag outside your car, or an enclosed space and the solvent will completely disappear.
If the surface is adsorbent, then a masking color is the only way to “remove” it. I keep spray paint in common utility colors like Metro brown, cable box mint green, white, and black for erasing graffiti in my self-defined neck of the woods (59th, Charleston, 49th, Admiral, sometimes up to the old folks mailbox at 47th.)
SDOT and Metro seem to respond quickly to graffiti, but I tackle problems in the ‘hood myself.