that's so cool that you posted this today because i've been knowing i wanted to teach sign to my son since before he was born and he's only 4 months old now.(so i have awhile to go before i even start! (at least two months)) but just today i wanted to look online and see if other momma have been teaching thier infants!
so anyway i recommend the book "sign with your baby" by j. garcia
i bought it from bn.com and it came as a kit with a great video and quick reference card, great for caretakers!
they used the milk sign for nurse. seemed simple enough unless you think later down the road that would get confusing with cow's milk?
you are thinking of teaching your infant? have you started? what age is your child?