A good friend of my sister's signed with her son. He did great and knew alot of signs before he could talk.
The only problem was I was babysitting one time and he kept signing that he wanted his bottle but I didn't know that's what he was doing!! He kept screaming and screaming. Finally when his mom picked him up she told us that was the sign for bottle. I felt so bad because I'm sure he was thinking we were ignoring his request. She had told us he had just eaten so he wouldn't need a bottle. But, I guess he wanted it for comfort. Poor baby.
So, just make sure your babysitters know the signs too