Mr N and I were rather half-hearted in our attempts at using signs while talking to Miss E. I think we pretty much just did the sign for "eat." Personally I guess I had a hard time believing it would work and that E would ever use sign language to communicate. Well lo and behold, one day Miss E kept doing some movement with her hand by her mouth. I realized, "She's signing EAT!" This was followed by much celebration!
At first E would cry and sign "eat" constantly until I put her in her highchair. Then after a day or two, once she signed "eat" (not crying) and I acknowledged it, she was fine. She understood that I understood her and would feed her. THEN she started signing "eat" ALL the time, even when I knew perfectly well she wasn't hungry (i.e., lunch was 10 minutes ago). She was kind of using "eat" as a catch-all sign because it was the only one she knew. So I taught her "play" and am currently trying to teach her "full" and "all done" (do you think she'll stop throwing food on the floor when she's done eating once she's done eating??? that's my hope!)
Image credit: http://www.babysignsbymaureen.com/