I do signing in my daycare I took a class on it as well. They say that a good time to start it is around 8 months. You may not see anything receptive till later on. But you will be suprised how much frustration and anger can be alleviated when a child can express themselves in a way where they are understood.
It really does help before they are able to speak to have communication with you. It also reduces biting / hitting etc. I know with my daycare kids it really helps them and myself. I also watch special needs children and they are much happier when we can understand each other.
Below are some links where you can get some more information on baby signs. Start with one word at a time. I usually start with words like " more, please, up. People will tell you that it will hinder their speech. It actually will help them.
Thing signing is a great way of communication. I have 2 boys 13 and 15 and when we are in the store and they are doing something i don't like. I can do the sign stop and they know. You can communicate to them things in a quiet calm manner. If we don't challenge them to communicate with you then that can set them back. When we always get what they want without requiring them to communicate, then they don't have a reason to.
It will take awhile to learn but you will be amazed one day when your child just out of the blue will sign to you. If you want more assistance you can email me offlist. I have child in my care who was adopted at age 3 has downs. I have had him since he moved to the USA. Within a 1 1/2 along with his mom we have been extremely successful in teaching him how to sign and communicate with words. I can communicate with him very well and he is such a happy and wonderful child. I have had numerous successes. One non-verbal child who has taken me 6 months he is 3. But he finally will say More, and signs it along with eat and please. It can't hurt to try it but you need to be consistant.