The folks over at Unshelved ran a few strips that made chuckle about the possibilty of ghosts in libraries.
So if you feel cold spots in the library, detect irregular electric fields, or notice that your office supplies disappear and books are rearranged, you might have ghosts. Or you just might have a library with a wonky HVAC system, unstable wifi, and patrons who borrow pens and “re-shelve” books to be helpful.
However, if these occurances cannot be easily explained, you might want to see if Ghost Hunters would like to investigate.