A standard "cut mark" or "signature delimiter" is used to indicate where message text ends and a removable signature begins. The Bat! will recognise this mark when you reply to a message and will cut away the mark and any text below it from the original text. This cut mark is a simple sequence comprising a new line, two dashes, a space and a new line. Like this:

<new line>

--<space><new line>

<new line> means "press return"

<space> means a single press of the space bar.

In an OpenPGP signed message, OpenPGP modifies the cut mark to have a preceding dash and space, i.e.

<new line>

-<space>--<space><new line>

This is by design.