1. One's name as written by oneself.
2. The act of signing one's name.
3. A distinctive mark, characteristic, or sound indicating identity: A surprise ending is the signature of an O. Henry short story.
4. (Abbr. Sig. or S.) Medicine. The part of a physician's prescription containing directions to the patient.
5. Music.
   1. A sign used to indicate key.
   2. A sign used to indicate tempo.
6. Printing.
   1. 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.
   2. A large sheet printed with four or a multiple of four pages that when folded becomes a section of the book.

[French, from Old French, from Medieval Latin signātūra, from Latin signātus, past participle of signāre, to mark, from signum, sign. See sign.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.