I used a piece of tracing paper the other night to print my exposure times onto some contact sheets and it ended up looking really cool. But of course that's white...

Writing your name on acetate with a nice black ink pen, and then copying this onto a high-contrast film (with as much density in the blacks as possible) would give you two different signatures; one to use in light areas and one to use in dark areas. Something like Worker's flash-light would have to be devised of course.

Imagine the possibilities with color papers and different colored inks, gels, lights...

It'd be really cool to just find some pen-light with a really narrow beam and you could sign your print directly.

Lastly, how about a rubber stamp pressed on a pad of Farmer's Reducer. But what chemical to create the black???