In my experience, Bill isn't a talker during the autographs portion. He's jovial and such on stage, but when the signing time comes, it's cattle-call, quick line stuff. Say "thanks" and "nice to meet you" and... that's about all, really. Don't expect much of anything from him. He's been doing about a half-dozen of these, minimum, every year, for the past 35+ years. He's signing 800+ autographs in an hour in rapid succession. Go in with that reality in your mind and you'll be alright. 
