I have heard about sharpies, layout fluid,and ink pads, but I haven't heard about anything permanent.
Some cases are diffrent enough to be readily distinguished from the parent cases, others not so much.

A 300 blk is not a issue, as it is diffrent, a 6x45 is as it is not that diffrent from the 223 parent case.
222 from 223, not that big a deal as neck is longer, mongoose has a diffrent shoulder angle, etc..
But..cleaning the brass will remove markings and dyes over time.