I'm sure many of the current movies out today, in an effort to obtain as much realism as possible, hire consultants to ensure the sign language used in movies is as accurate as any other language used by characters.
However, I'm watching the Vincent Price classic The Tingler and I can't help but feel that the sign language used by the deaf mute at the beginning of the movie was just some crazy hand gestures ad-libbed.
Does anyone know, for sure, if they were using real signs for that part?