Source : Free On-Line Dictionary of Computing

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)