A signature is a special combination of data assigned to a person for identification purposes. A signature is largely equivalent to an electronic business card that can be attached to a document, such as an e-mail or a fax.
In the case of e-mails, this is referred to as a mail signature. The prerequisite for such a signature is an e-mail program that contains this option. Mostly, such mail signatures consist only of name and e-mail address, sometimes the postal address and a link to the homepage of the author are added. Signatures are meant to replace the headers that some email programs automatically truncate upon receipt.