double bucky = D = down

doubled sig [Usenet] n.

A sig block that has been included twice in a Usenet article or, less commonly, in an electronic mail message. An article or message with a doubled sig can be caused by improperly configured software. More often, however, it reveals the author's lack of experience in electronic communication. See B1FF, pseudo.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.