Is it on your inner fenderwells? Every state has a different kind of traffic line paint, but you might need to use something as agressive as lacquer thinner to clean it off, but I would try some mineral spirits first. I would wet a rag and then wipe the area down to loosen it up. You might also try a pressure washer at one of the coin op places as you might be able to blast a good amount of it off. Other than that some undercoating sprayed in there will hide it and make it look like new again. For the stuff that's on the outside, I would try clay first and then some mineral spirits
I should have clarified that it is on the inner fenders. I appreciate the replies. I've actually have pretty good luck so far with some 1Z Industrie-Reiniger W99 APC, an old red shop rag, and some good 'ol fashioned EG (elbow grease).