One's name as written by oneself. The act of signing one's name. A distinctive mark, characteristic, or sound indicating identity: A surprise ending is the signature of an O. Henry short story. Medicine The part of a physician's prescription containing directions to the patient. Music A sign used to indicate key. Music A sign used to indicate tempo. Printing A letter, number, or symbol placed at the bottom of the first page on each sheet of printed pages of a book as a guide to the proper sequence of the sheets in binding. Printing A large sheet printed with four or a multiple of four pages that when folded becomes a section of the book.