Way back when I was student teaching, I also took a night course in American Sign Language (ASL) because I've always thought that it is a beautiful language. I picked up just enough sign to teach some basics to my students when I taught Kindergarten, which was fun, but very limited.
When I found out that I was going to be a Tante, I was excited to brush up on and learn more ASL to use with my niece. At almost 18 months now, she has a vocabulary of about as many spoken words as signs...and some definite favorites. It took about two months for her to pick up "finished" but she was signing "more grapes" within a week of my introducing the sign for grapes. She loves champange grapes and rarely wants to be finished eating them!
There are so many great resources for ASL and baby sign language; some of my favorites for sharing with my niece are the board books by Linda P. Acredolo. Good sign dictionaries show the torso and face of the person signing, taking into account that signs are done in specific locations (from top of the head to the waist) and include facial expression. Linda's books not only show torso and face, they do so with actual babies making the signs. Babies love looking at other babies!