What pen/ink on skull cap?

So I got a couple of stag in Scotland and they're boiling out the skulls. I saw some old skull caps on boards over here and they have writing on them. After I bleach the skulls, what kind of pen/ink should I use on the bone? Just a permanent marker would look a little tacky and I would think it would disperse and soak into the bone.

Thanks in advance for y'all's help.