Last night Bean signed "banana". It was the first definitive sign where I could be sure that she understood that the sign meant banana and wasn't just mimicking our hand motions. She signed unprompted to ask for some banana.
It was freaking incredible, I tell you. She's so awesome.
(Oh, I should note that her sign is a very crude approximation of the sign we've been doing with her, but nonetheless, it was clear that she was trying to sign to us, and that's the important part.)