[A] signature block is conventionally delimited from the body of the message by a single line consisting of exactly two hyphens, followed by a space, followed by the end of line (i.e., in C-notation: "-- \n").

As of now, when reflowing, wrap deletes the space that follows the two hyphens, which leads to failing to recognize the signature (for example, if some other program is used as a pager after wrap).

Probably, wrap should just skip ^-- $ lines altogether.