I wonder how it would distinguish between the many dialects in use in the US. Granted, a lot of the adult population does use ASL [1], but lots of times children grow up using one of the Signed English[2] variants, which vary from state to state.

[1] http://en.wikipedia.org/wiki/American_Sign_Language

[2] http://en.wikipedia.org/wiki/Signing_Exact_English

[Edit: links]