I frequently hear new mothers asking about baby sign and if it's beneficial/harmful/worth it. I never really knew anything about it until my two older sisters started using it with my nephew (one sister nannies the other one's child). They had such wild success with it that when I was looking forward to the birth of L.H., there was no doubt in my mind that I would use it, too.
Let me just clear up a few common misconceptions that I hear. Most people are convinced that teaching your baby sign will delay their speech development. There are no studies that have shown signing causing any speech delay. In fact, it seems that signing gives babies an earlier understanding of language and a bigger vocabulary once they do speak. Not to mention that if you use real signs from ASL or IS (or any other real sign language) instead of making up more "baby-friendly" signs, then you are actually giving them some basics to communicate with those who use sign due to deafness or other special needs.
Think of it this way: my seven-month-old was able to tell me when she wanted milk or when she needed a diaper change. How many times are parents left guessing as to what their infant or toddler wants? How many parents have wished that the kid could just talk so that they could fix whatever it is that is making the child scream?
L.H. is hearing two languages at home (English from me and Hebrew from N.) and this is causing some people to be concerned that she will not talk until later. Aside from the fact that this concern is unfounded (at 15.5 months she has a vocabulary of nearly 20 spoken words), she also has the signing to rely on. She has basically the same number of signs and spoken words and for the most part they don't overlap. But imagine if she didn't speak until the age of two or beyond - with the signing, she would still have the words she needs in order to communicate with us.
Many people think that signing will be too difficult for them (or the babies) to learn. Keep in mind that you're not learning the full language; you're learning individual words and the alphabet in order to spell words that don't have a sign. If I actually encountered someone who communicates through sign then to them I would sign like a baby - no sentences or structure, just disjointed thoughts. You can learn as few or as many words as you want. I started with the things that were most important to her and as time goes on, we add more and more. Whenever she shows interest in something, I look up the sign so that she can talk about it.
The best part of it all is that L.H. can communicate with us and is confident that her needs will be met without her screaming.