A signature block (often abbreviated as signature, sig block, sig file, .sig, dot sig, siggy, or just sig) is a block of text automatically appended at the bottom of an email message, Usenet article, or Internet forum post.
"Traditional" internet cultural .sig practices assume the use of monospaced ASCII text because they pre-date MIME and the use of HTML in email. In this tradition, it is common practice for a signature block to consist of one or more lines containing some brief information on the author of the message such as phone number and email address, URLs for sites owned or favoured by the author—but also often a quotation (occasionally automatically generated by such tools as fortune), or an ASCII art picture. Among some groups of people it has been common to include self-classification codes.
|\_/| **************************** (\_/) / @ @ \ * "Purrrfectly pleasant" * (='.'=) ( > º < ) * Poppy Prinz * (")_(") `>>x<<´ * (email@example.com) * / O \ ****************************
Most email clients, including Mozilla Thunderbird, the built-in mail tool of the web browser Opera, Microsoft Outlook and Outlook Express, and Eudora, can be configured to automatically append an email signature with each new message. A shortened form of a signature block (sometimes called a "signature line"), only including one's name, often with some distinguishing prefix, can be used to simply indicate the end of a posting style or response. Most email servers can be configured to append email signatures to all outgoing mail as well.
The Usenet standard RFC 3676 specifies that a signature block should be displayed as plain text in a fixed-width font (no HTML, images, or other rich text), and should be delimited from the body of the message by a single line consisting of exactly two hyphens, followed by a space, followed by the end of line (i.e., in C-notation: "-- \n").See Charles H. Lindsey: Usenet Best Practice, 2005, and also RFC 3676: The Text/Plain Format and DelSp Parameters, section 4.3, 2004, and RFC 1849: “Son of 1036”: News Article Format and Transmission, section 4.3.2, 2010 (first circulated in 1994). This latter prescription, which goes by many names, including "sig dashes", "signature cut line", "sig-marker", "sig separator" and "signature delimiter", allows software to automatically mark or remove the sig block as the receiver desires.
In addition to these standard items, of various sorts are often automatically appended. These are typically couched in legal jargon, but it is unclear what weight they have in law, and they are routinely lampooned.
Business emails may also use some signature block elements mandated by local laws:
While criticized by some as overly bureaucratic, these regulations only extend existing laws for paper business correspondence to email.
However, a tearline standard for FidoNet was included in FTS-0004 "FidoNet EchoMail Specification" and clarified in FSC-0068 "A Proposed Replacement For FTS-0004" as three dashes optionally followed by a space optionally followed by text.