We've been working more with C on signing for "More" and "All done." J picked this trick up pretty early, but we were more consistent with her to begin with.
A few days ago Abbey bought a box of Cheezits. I don't think Cora had ever had any before, and it's quite obvious that she likes them very much. If you hold out a handful of crackers, she is not content to take one, or two, or even three; she wants all of them in her mouth, poste-haste.
Last night I took both girls to the park. After a while I took C back to the car to change her diaper. To keep her pacified while changing, I handed her a Cheezit that I found in her car seat. She gobbled it up, and then immediately started aggressively signing "more." It was the first time I've seen her doing that so clearly. Sadly, I didn't have anymore crackers with me so she got pretty upset. Still, it's always a pretty amazing thing when you see a baby trying very hard to communicate her desires to you so clearly.