We're beginning to have students return textbooks to the library as the school year is coming to a close and need to keep the books in numerical order (yes, I noticed that two books are not in order after I took the photo!).
My husband came up with this humourous sign, and I'm suprised at how many of our students understand the reference! Sometimes I put up signs just for my amusement, but this one seemed to reach more age groups than just mine.
A printable version (purple font) of this sign is here --> www.flickr.com/photos/vblibrary/7414544704