I like this set up for a guest book signing table. I have a vintage trunk that looks good for cards with a sign. The "love note" sign is a good idea. The trunk would work well set up on a vintage chair or stool as well.
You've heard about a coffee bar; what about a tea station? I always think its important to add personal touches to weddings.and I know you love tea! You could DIY it by adding hearts to the tea bags in multi colors places in mason jars.