I thought it was pad print. If it is try some dot4 brake fluid, castrol super clean, easy-off oven cleaner, or chameleon model paint remover. One of them should work. Can lift some types of paint/ink and does not damage abs. So you can get rid of legend and not loose texture. There's a good chance you might have some of those items around already. If it's lasered then there is nothing to do but remove the surface with abrasive as it is effectively burned in.
I wouldn't recommend any of those. ABS will be ruined by every one of those things you listed. The damage is not always dramatically apparent, but that's always been the trouble with ABS, the slow death.
OP, you're better off just buying a set of blank keycaps. They have ABS blanks at WASD, and PBT blanks on ebay sold be Geek feng
If you are buying black, I'd recommend the PBT because black will easily turn shiny if they're abs caps.
If you are buying lighter colors like white red yellow blue, then I'd recommend the ABS, because even if there is some shine on those colors, it doesn't look bad at all.
The reason I'd recommend WASD white, is because the PBT white that feng sells isn't really white. It's more of a white shifted blue/violet, due to the UV dye they must've used.
