Question: I would like to know when is a good time to start teaching your baby sign language. I heard they won't start signing back to you before 6-7 months so starting before 3 months might be pointless. Any thoughts on when you think would be a good time to start for your sake as well as your baby's?

Answer: 
Just do it as normal all the time.

They pick up everything all the time.

That is how children learn by seeing, hearing and experiencing things.
You might as well start early to grow your own vocabulary, and to build the habit for yourself.