First, mask off the general outline and surrounding area. Then, use some masking putty (should be able to find it at any local hobby shop, like Hobby Lobby or Hobbytown USA, in the states that is). It's just a putty that you can paint on to get any shape you want, and it dries into a latex-like consistency. It'll be perfect for the non-straight edges of the letters.
Then just spray paint the color you want, wait overnight for everything to dry good, then just peel off the mask. Should look great!