Depending on just how heavy of a coat it is and if I felt I could remove it, I'd start with acetone or nail polish remover, followed by clay and see what that does.
You can get more agressive but if you do, you may cut into original paint as well.
I would try with something like WD40 first and see how much comes off. You'll need to scrub it fairly briskly to get any off. You can try Goo Gone to get it off as well. After that, as suggested, a clay bar and elbow grease to get the rest. Good luck.