I designed a recess on the top of the holder for a label. It is a sort of spiral shape that keeps a fairly even offset from the through holes.

I designed the label quickly in Inkscape, using my favorite font, Arial. I will start by just printing it out on a label sheet, cutting it out and sticking it down. Might not last, but it shouldn't see too much wear and tear so it actually might be fine. If I wanted to go ape shit I could pour clear epoxy over it, would probably look terrible if I didn't go to the trouble of vacuum degassing and curing in a pressure tank.