A signature (from Latin signare, "sign") is a handwritten (and sometimes stylized) depiction of someone's name, nickname or even a simple "X" that a person writes on documents as a proof of identity and intent. The writer of a signature is a signatory. Like a handwritten signature, a signature work describes the work as readily identifying its creator.

Function and types of signatures

The traditional function of a signature is evidential: it is to give evidence of:

1. The provenance of the document (identity)
2. The intention (will) of an individual with regard to that document

For example, the role of a signature in many consumer contracts is not solely to provide evidence of the identity of the contracting party, but rather to additionally provide evidence of deliberation and informed consent. This is why the signature often appears at the bottom or end of a document.

In many countries, signatures may be witnessed and recorded in the presence of a Notary Public to carry additional legal force. On legal documents, an illiterate signatory can make a "mark" (often an "X" but occasionally a personalized symbol), so long as the document is countersigned by a literate witness. There are many other terms which are synonymous with 'signature'. In the United States, one is John Hancock, named after the first of the signatories of the United States Declaration of Independence.

The signature of a famous person is sometimes known as an autograph, and is then typically written on its own or with a brief note to the recipient. Rather than providing authentication for a document, the autograph is given as a souvenir which acknowledges the recipient's access to the autographer.

In the United States, some states' legal definition of a signature defines a signature to mean "any memorandum, mark, or sign made with intent to authenticate any instrument or writing, or the subscription of any person thereto." In the context of one particular statute, a signature doesn't have to be the popular notion of a written name, but may be other methods of authentication; the intent of any mark or memorandum makes a signature.

Many individuals have much more fanciful signatures than their normal cursive writing, including elaborate ascenders, descenders and exotic flourishes, much as one would find in calligraphic writing. As an example, the final "k" in John Hancock's famous signature on the US Declaration of Independence loops back to underline his name. This kind of flourish is also known as a paraph.