Everyone with a child should read this book before hopping on the baby sign wagon. This is the original book by the professors who "discovered" baby sign with their children. I like how it points out that baby sign is not about teaching a second language or continuing it for the rest of their lives. It's about relieving the frustration of a baby able to understand but unable to communicate back because their vocal muscle control isn't good enough. It's about building relationships so a child can ask for things instead of throwing tantrums. It's about helping your baby's brain get started in language patterns earlier, which impacts where they are later in life. According to the study these women set up, baby sign kids maintained an advantage of one grade level of IQ over peers.
I really love baby sign, and I say take it to the source.