i use sharpie. it might not bond with the plastic, but it will still be awesome if you don't abuse it (i.e. throw it, keep it in a bookbag, brawl hard with it, etc.).NOTE: if you use silver sharpies, remember to only go over it with ONE COAT. if you do 2 or more, it will look splotchy and amateurish.model figurine paint would probably work.