We started signing to Calvin around the time he turned 6 months. I didn't get really serious about it (with the baby signing videos) until around 9 months. And just the other day, I saw proof that he' starting to get it. Not that he's keying in on the ones that I'd like him to (like "more", "all done", "please")-well, maybe he is and they'll be next-but he's following suit to his big brother. Just like William, his first sign is "dog" (two slaps on the thigh). He even adds the sound "doh" to it (o; I guess my boys love their dogs.
Here's my attempts at capturing it: