[Bicycle Bob]

Here's the trick to cleaning the lettering from Coroplast:

Acetone or lacquer thinner will quickly melt most ink, but if you let the solvent evaporate, you just have a different mess. Immediate towel drying is the key. You can use two hands, one with a wet rag, followed immediately by a dry one as you scrub across a section in broad zig-zags. For smaller jobs, just take a paper towel, fold it a bit, and hold it on your hand by gripping between your fingers. Wet the edge at the heel of your hand, and use the finger side for drying. You just rub the spot you want to clean with the wet towel, and do hand-waving motions from the elbow while slowly progressing across the surface.

BTW, this is a useful skill for anyone who uses solvents to prepare surfaces for bonding. The commercial grades usually leave some oil behind if allowed to evaporate, even if there was none there before.