If it was a bona fide signed message, it would begin with:
"----- BEGIN PGP SIGNED MESSAGE -----".
The bit at the bottom would be essentially similar, though with newlines at appropriate points. The garbage-looking bit, in a real signed PGP message, would be unique to the message text and to the sender's encryption key.
The "Authentic Sender" bit, whatever it is, is not PGP.
This looks to me like spam designed to appear digitally signed (to an unsophisticated spam filter).
Incidentally, GnuPG is an open-source free substitute for PGP.
Edited for accuracy
Last edited by Tuba Mirum; 2nd October 2004 at 07:57.