Have always wondered about it myself, but only know a few signs beyond the alphabet. Helped greatly though at my cousin's wedding (bride and groom and several guests were deaf).
That said, I LOVED the last version of BIG RIVER with the half-deaf/half-hearing cast. Beautiful, beautiful, beautiful. Especially the 2 moments when they used the non-hearing people's own voices to get a point a cross. Poignant.
And signed performances of any show I do are often my favorite, especially if I'm calling from the booth and can view most of it!
I know this really doesn't answer your question, just wanted to share.
Erin