Butane torch, be careful with it, but it's the portable heat gun. If you lack a good hardware supply store, I know some auto stores carry em (used to work at a Checkers/Schucks/Kragen and we had em on hand in the tools section bottom shelf, most likely where you'll find it).
I've seen the ads for all the different kinds of removers and crap, but never heard anything decent about them. You may want to research some threads at
Signs 101 Home - Signs 101 the people there aren't the greatest sometimes, but the information is valuable. I personally haven't had good luck with the plastic razor blades, seemed to take a lot of work to get them under. I use a regular razor blade instead now, and a lil chisler for smaller letters.