Jeff and I spent many months signing to Judah, Salem and Adia as babies and they all picked it up after a few months. Well okay, Salem only did it when he felt like it, but the other two use(d) it all the time. It takes 2 or 3 months of consistently signing to them before they finally produce that first sign. It's pretty exciting when they FINALLY do sign back.
Here is a video of Adia showing off her communication skills asking to do her favorite thing . . . eat and eat some more! She is 16 months old and has been signing for about 3 months. If you've never seen baby sign in action, it's pretty fun to watch. Here she is, enjoy! (Sorry about the blurry spots in the video. It may have had something to do with little boys, a hot tub and our camera! At least it still works.)