I was looking for a non-permanent way to color my stamped letters on my receiver and a thread on the hide suggested a China Marker. It seems to do the trick and looks like it's more permanent than I though it would be. If I like it enough and it ever comes off, I'll probably paint it in. For now though, it looks good.
Edit:
Did the Fire and Safe engravings
Edit:
Did the Fire and Safe engravings