It's only Girls getting books right? And guys get the pens? Because it would reason that mitch would know who we all are, so he could just hand books out to the ladies without any name calling, and then the guys just keep their pens and sign. If they each have a different color pen they could just sign a little note or something of their choosing into the books, and then it'd be easy to coordinate the dances without spilling any names. That and then everyone has their personalized keepsake like you mentioned~