@BOOKHOUSE Bragging rights, maybe? If you're pretty sure they're on some social network you're also on, you could write a post that says @ so-and-so is clever and solved the such-and such puzzle!

@BOOKHOUSE Only 3 options, an image, a song, or a story.

@retech morning me thinks some sort of proof of completion and solving stuff certificate one can download. That is not quite it, but it is closer.

Thank you for being my idea bouncing board.

@BOOKHOUSE Options are certainly narrowed with this one.

@BOOKHOUSE You could give out something actually physical. Like a set of coordinates that gives a location to pick something up.