What is the rest made out of? Metal, plastic? Knowing that, just go to a hardware store and find some spray paint. One can of primer, one can of black. There's a lot of spray paint out there, but it can range from use on plastic, metal, wood, all in one. Try to get the most specific kind for your rest. Spray primer first, then black. Or save about 10 dollars and use a sharpie like GMMAT said.
id take any old paint off first if there is any. then prime it using a dark grey, then use rustoleum matt/flatt black.
