When we were there in October we saw Vanellope and Wreck-It-Ralph. As we were in line for them, a CM came around and gave us each a Wreck-it-Ralph card, kind of like a baseball card. We placed that in the signature area of the book which I assumed was the intention behind it. I know that Buzz Lightyear doesn't sign but rather has a stamp that contains his signature, at least that was my experience with him a few years ago.