It doesn't remove it, but changes the content type so its displayed normally.
What is the use of an ASCII-displayed pgp signature?
I use Pinepg to check signatures/send/recieve email.. when its attached, and you have a DISPLAY-FILTER set in pine to automatically deal with them.. it gets missed.
Ie:
display-filters=_BEGINNING("-----BEGIN PGP MESSAGE-----")_ /usr/local/pinepg/decrypt _RESULTFILE_ _DATAFILE_ _PREPENDKEY_,
_BEGINNING("-----BEGIN PGP SIGNED MESSAGE-----")_ /usr/local/pinepg/verify _TMPFILE_ _RESULTFILE_