The last time I went, which was the first time for DD, we used a colored Sharpie. We have the characters sign in the Disney's Jr Encyclopedia of Animated Characters. I plan on using a different colored sharpie for each visit. That way we can know which characters we saw on which date. I also had DD write her name in the book using that color. It'll be neat to see her signature change through the years.
In any case, for the fuzzy characters, I would uncap the pen for them and hold it out for them by the cap so they could just take the pen and sign.
I suppose I could switch over to a crayola washable marker. I just have to make sure it won't smear in our book.
The interesting side note is that when we saw Silvermist at Pixie Hollow, she wanted a blue colored pen, lol! Unfortunately she had to use our only writing instrument - a pink sharpie.