we've been signing with tristan for a few months now. hes been reacting to the signs for a while, especially "milk" (you can look up signs here http://commtechlab.msu.edu/sites/aslweb/browser.htm ). Tonight when i was telling him it was time to eat, and signing "milk", david noticed his hands were making the sign. we tried again, and sure enough, when i signed "milk", so did he :)
He has also been saying "ma" or "mama"intentionally when he gets agitated. usually its just ma-ma-ma babbles, but when he wants me to get him it is purposeful.
he also loves talking on the phone, and gets excited when it rings.
he is learning so much everyday, i cant believe how much he picks up.