I liked the movie, but I haven't read the script, but I would think the script would look much like a normal script, with dialogue blocks and all. It's not like they didn't speak, they just spoke with sign language. So you would need what was being said in sign language to be blocked out as...
I used to have a screenplay formatting guide online that crashed about 6 years ago. I finally got it up and running again and wanted to let you guys check it out: www.screenreads.com/formatting
Let me know what you think. I hope people here will find it useful.