You can buy a pen in the office supply stores. It's designed to write on mylar prints, but it writes on anything, CD's, glass, etc. It looks like a fancy (reddish color) felt tip pen. The one I have is 20 years old and I'm sure they still sell something equivalent. It's permanent/doesn't rub off. Here's what is written on it: STABILO-OHPen196P SUPERFINE S, wasserfest permanent, Nach Gebrauch verschlieBen. Try saying that mouth full. It's the best permanent marker I ever had, writes black - the reason I still have it. I'm not sure if it can be removed, though, maybe with Acetone.