A month or so ago, Will walked in, carrying Vivian and asked "What does this (clapping his hands) mean in sign language? Vivian has just done that." We determined that she was not a sign-language prodigy, but had learned to clap. :)
Today though, as I was eating an apple, Vivian moved her hand to her mouth the same way she does when she tries to get something in there with the whole palm. She repeated this a couple of times during the day, always when I was eating something and she wanted to try some.
She is truly our daughter. Her first sign is "food"!