Cite
 
sig block: /sig blok/, n.

[Internet and Usenet; often written ‘.sig’ there] Short for ‘signature’, used specifically to refer to the electronic signature block that most Unix mail- and news-posting software will automagically append to outgoing mail and news. The composition of one's sig can be quite an art form, including an ASCII logo, one's choice of witty sayings (see sig quote, fool file), or even source code for small programs about which the author wishes to make a statement; but many consider large sigs a waste of bandwidth, and it has been observed that the size of one's sig block is usually inversely proportional to one's longevity and level of prestige on the net. See also doubled sig, McQuary limit.