How to personalize existing chips

[Coelacanth]

This is from somebody I work with. Any suggestions? I saw a post or two about labels, but does anyone know of a place that will engrave or stamp existing chips?

__
I have a set of poker chips with sentimental value and I'd like to put some initials on each of the chips. The end result should be nice and permanent but it doesn't have to be perfect. I'm not sure how to do this, I guess possibilities are engraving, stamping, or even getting a nice calligrapher to just write on the chips. Any suggestions? Does anybody knows where this can be done?