Signature block (.signature)
The block of text appended to every post and email, with its own delimiter and an unwritten length limit.
Unix mail programs and newsreaders automatically appended ~/.signature from the home directory. It began with the line -- — two hyphens and a space — so reading software could spot it and strip it when quoting. The trailing space was routinely eaten by some client or other, and the feature went with it.
The norm, known as the McQuary limit, was four lines of at most 80 characters. It was flouted constantly by ASCII art, Monty Python quotes and lists of every machine the sender had an account on. Every post was copied to thousands of servers, so a ten-line sig was quite literally someone else's disk space.