The book probably was at the bottom of a pile of 14 library books, accidentally got picked up and dumped in the bibliovore labeled “Return Books Here.” […] [Y]ou meekly approach the library to find out what they would do with a book that wasn’t theirs. […] [I]f the marking is on the inside, the marking that has your name or the name of the department on it, it disappears.
Source: wiktionary