The Jargon File (version 4.4.7, 29 Dec 2003):

doubled sig
 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 Free On-line Dictionary of Computing (30 December 2018):

doubled sig

   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 BIFF, pseudo.

   [Jargon File]

   (1994-12-07)