Hi there! Good question to ask! Yes I used sign language with both of my kids and they both picked it up very quickly and still use it today. Yes there are reports that say that the baby can communicate faster and have a higher level of vocabulary b/c of sign language and I believe it, b/c it worked for us. Think of this, your child is screaming, fussing, upset over something and you can't figure it out. Why? Because he can't communicate it to you just yet. I took a sign language class in college and had an American Sign Language book that I kept so I just used that and it worked great for what I wanted to accomplish.
There is not right or wrong age to start, I started with my little girl around 6 months, and my little boy probably around 4 months. We started with simple signs as "more", "drink," and "food" being very broad with the signs. When my daughter started eating puffs and small finger foods is when the more sign clicked and she started to put it together. We just kept repeating the sign and asking if she wanted more as we were referring to her puffs or snack or food in general. When it came to drink, we asked if she wanted a drink, and showed the sign for drink. Constant repetition is key, that's how any language is learned.
My kids were more calm and we were able to understand them and they were able to understand us. Kids can understand verbal language early on, but just the communicating verbally is what is slow to develop. They understand signs, body language, tones in your voice, so why wouldn't this work.
Yes they can make the signs with their little hands. You're working with little hands with simple signs that are very easy for them to form. My daughter actually adapted the sign for more, but we knew what she wanted. Any of the parent websites out there have links to learning how to do a few signs. You take it as far as you want to go with it. My kids are 3 and almost 2 and they both use the signs still. My daughter not quite as much but she is 3 and still remembers the signs we taught her.
I think it has helped their language skills. My daughter at 15 months was talking in 2 and 3 words sentences and by the time she was 2 she had an ENORMOUS vocabulary and was talking sentences left and right. (Though she is a girl and some say girls develop faster in their language skills than boys.)
So overall, I do recommend doing this, why not!!!
We taught them the following signs: more, food, drink, milk, wait, water, please, thank you, yes, no, potty, music, sleep and I think that's it. Some stuck more than others, and for the most part as they did the sign they said the word too.
Good luck!
A. B