We had some pinstripes on our truck when we were looking at it which we hated. Before I bought it I made them take the pinstripes off. The people in their body shop (and they had a full service body shop, not just mechanics) said a hair dryer was usually the best route 9 times out of 10 and then they used some sort of solvent on any remaining glue spots. Unfortunately I don't remember what the solvent was. I've heard some people say that 'Gunk off' (or something like that) works great on old glue. Just test ANYTHING like that on a hidden area of paint (like in your doorwell) before you put it on the exterior.