Baby sign is such a hot topic in parenting right now . This is only my perspective on baby sign and everyone is welcome to agree or disagree:
It's a natural fact, babies are going to begin communicating through gestures before they communicate through words. Think about what your baby tells you when he points at something or lifts his arms to have you pick him up. These gestures are obvious, clear and universally understood. Babies do pick up on sign language earlier than spoken words because it's easier for them to make the motor movements with their hands and body than to coordinate their mouths for speech. However, unless there is a reason for your baby to learn a formal sign system like American Sign Language , it is not necessary to spend money on books, videos and classess in order to learn how to teach your baby to sign. Just pick what comes naturally. For example, the ASL sign for 'more' is made by touching the fingertips of both hands together. This is one sign that is very commonly known; however, I think a child's message would be equally clear if he were to to point to the palm of his hand to request 'more', which is a much more natural gesture for this request.
The argument against this strategy is that common ASL signs are known by many other people including childcare providers, so if you teach your child the formal signs, they will be understood by others as well. I feel that if you're using natural gestures with your child, than any other adults interacting with your child will naturally understand their meaning as well.
A child who learns language easily may learn to use gestures to communicate for a brief time as a bridge to spoken words, but should then quickly be learning to say those most important spoken words. To me, it's not worth the effort of teaching your baby a formal sign system that will be used for just a few months, when there's a much easier alternative available.