We did with DD and are signing at 8 month old DS - who is watching and appears to recognize, but not imitating yet. We loved it with DD. Saved heaps of frustration when DD could get her simple requests across and I credit it with her early speech development. We didn't get any specific books or vids, but I knew a fair bit as I have a close friend who is deaf who has taught me auslan. If we didn't know a sign for something, or it didn't exist (eg. For a specific toy), we'd just make up a sign that made sense to us and DD could manage with her level of motor skills. After all (unless of course your child does have contact with deaf people), it doesn't matter if it's the 'right' sign, as long as you and your child understand each other.