Unique guest book ideas?

I saw one guest book where there was a huge poster sized bear tree (tree with no leaves) and a pad of green ink sitting at the table and each guest stamped their thumb print onto the tree and signed their name next to it and by the end of it, the tree was filled with leaves and then the couple framed it for their home. I thought it was so cute that I'm doing this for my outdoor wedding! Good luck, I hope your wedding is magical and everything you wanted!