Well, while I agree that it could be a useful skill, Larceny as a skill covers all things illegal, and forgery also fits under Artistry (since replication does take artistic talent). I don't think forgery by itself is useful enough as a skill on it's own however. I can think of uses for it, but not enough applicable ones that could actually qualify it for it's own unique skill.
I mean, I'm not opposed to criminality in the game by any means ( as should be obvious ) however putting in a skill that would better fit into one we already have would be akin to adding a Legal Documenting Skill to understand and draft legal documents. Part of Artistry there, as well as the Law skill. Artistry isn't just for flowery stuff, writing is for writing novels, poems, speeches, etc, visual covers Illumination, Painting, Scultpure, Illustration, Drawing. Music covers composing and playing music as well as various instruments, Dancing covers choreography and perfoming. Artistry isn't just a foofy skill to perform with, it's listed the way it is since that is the most common usage for it, you guys can use your imagination for other uses, but if I try and include everything a skill can be used for, each skill will be multiple pages long.