Goof Off (United States customizers can find it in the paint/solvent/etc. section of Walmart, among other places -- I dunno about its availability in other countries) takes off symbol paint in seconds. The only thing it doesn't work well on is glitter, which I usually just scratch off with the tip of an X-acto. Remember that Goof Off's a noxious chemical that gives off nasty fumes, so use appropriate safety precautions if you give it a try, and rinse/scrub the bait really well afterward.
I used to use acetone, but it gave me lots of trouble. I find that Goof Off works better.
~Minty