Don't know the name of actor but.....how did he know how to sign??

I did watch that movie but I often wondered if that actor who does the sign lanauge really does sign in real life? I don't know his name but in that movie, he presented himself as a Deaf Mobster brother to Mobster who isn't deaf, and I remembered how smoothly he signed to his "brother" in that movie. I thought, "He had to know how to sign that way!". What people don't know is that it's not easy to fool the public that you could "sign" and it's damn near-impossible to sign so well that you could convince a Deaf person that you're Deaf. I'm Deaf and I've taught my wife everything I knew in sign language and she was so damned good at it that Deaf people actually thought she was Deaf. Anyway the point is, that actor, (if you could tell me that name, I'll be grateful, I think he played a part in Wayne's World part 1, at the end where he was repented and joined Wayne and said to Wayne's band, "Hi". He signed so good that I thought that he had to KNOW specific sign language that only Deaf people would sign. It's difficult to explain but it's like if you talk to someone, you'll know where that person is from by his/her accent alone, the same thing applied to sign language expect the difference is that how good you sign, if you sign so good but not up to the par equal to the Deaf person, that would meant you had Deaf person in your family or you had extremely close relationship with Deaf person. So, please let me know if he actually knew American Sign Language or not because that drives me crazy to wonder if he actually KNEW how to sign that way or just that he practiced his "signs".