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/