A one to n line ascii file which is appended to the end of email messages by mail programs such as Pine. Typically contains such information on the sender as name, email, homepage, often a ham radio callsign, a MBTI and sometimes a full postal address or other such location identifier. Suits may choose to include the most impressive version of their job title and corporate identity here. A short irreverent tagline, fortune, or other cookie is often included.

Unix users have historically tended to store this information in a file called .signature, which lead to it being referred to as either a "dot signature" or "sig file." Seasoned Internet users will find, with a few notable exceptions, that the experience and credibility of a correspondent tends to be inversely proportional to the number of lines in their signature.

A dataset which identifies an entity uniquely. In EW, this may be the RCS of an airplane. In intrusion detection, it is a set of packets which identify an attack (e.g. four SYN packets to separate ports may be the signature of a portscan).

Signature-based intrusion detection is most useful for detecting reconnaissance; a well-implemented covert channel should be completely undetectable to a signature oriented IDS.

A signature is a single section in a book with a sewn binding, either hardcover or paperback. It is a single piece of paper that may or may not have printing on it, folded and then trimmed at the edges, and sewn together, with other signatures, form the book block. A signature is generally 8, 16, or 32 pages, though it can be more or less.

One may identify a book with a sewn binding by noting that it is comprised of separate signatures, sewn together at the spine, rather than a mass of pages, glued together, and by the stitching between the center two pages of the signature, at the fold.

In most of the books printed before the 20th c., and some printed more recently, one can identify the first page of the signature by a letter at the bottom center of the first page of the signature. The signatures are lettered in chronological order, starting with A and going to Z, then from AA to ZZ, etc. This was done so that the bookbinder would know the proper order to sew the signatures together in.

Sig"na*ture (?), n. [F. (cf. It. signatura, segnatura, Sp. & LL. signatura), from L. signare, signatum. See Sign, v. t.]


A sign, stamp, or mark impressed, as by a seal.

The brain, being well furnished with various traces, signatures, and images. I. Watts.

The natural and indelible signature of God, which human souls . . . are supposed to be stamped with. Bentley.


Especially, the name of any person, written with his own hand, employed to signify that the writing which precedes accords with his wishes or intentions; a sign manual; an autograph.

3. Physiol.

An outward mark by which internal characteristics were supposed to be indicated.

Some plants bear a very evident signature of their nature and use. Dr. H. More.

4. Old Med.

A resemblance between the external characters of a disease and those of some physical agent, for instance, that existing between the red skin of scarlet fever and a red cloth; -- supposed to indicate this agent in the treatment of the disease.

5. Mus.

The designation of the key (when not C major, or its relative, A minor) by means of one or more sharps or flats at the beginning of the staff, immediately after the clef, affecting all notes of the same letter throughout the piece or movement. Each minor key has the same signature as its relative major.

6. Print. (a)

A letter or figure placed at the bottom of the first page of each sheet of a book or pamphlet, as a direction to the binder in arranging and folding the sheets.


The printed sheet so marked, or the form from which it is printed; as, to reprint one or more signatures.

⇒ Star signatures (as A*, 1*) are the same characters, with the addition of asterisks, used on the first pages of offcuts, as in 12mo sheets.

7. Pharm.

That part of a prescription which contains the directions to the patient. It is usually prefaced by S or Sig. (an abbreviation for the Latin signa, imperative of signare to sign or mark).


© Webster 1913.

Sig"na*ture (?), v. t.

To mark with, or as with, a signature or signatures.


© Webster 1913.

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