A roll of brown paper was donated, so I used it to put panels above each section of shelves around the walls. I cut 36 panels three feet long, and used an exacto knife to cut out shapes of something that could be found in the bookshelves below. The Statue of Liberty stands above books about the U.S. and the Alamo is above the Texas books. The project took about 3 hours from start to finish, including attaching them to the walls.
My purpose was simply for decoration, but in the three years I've had them up, they've become great traffic signs to direct students around the library. I tell students the fairy tales are under the castle; the sports books are under the basketball, the biographies are under the silhouettes of famous people, etc.