By default, Mailcrypt will supply a "comment" option to PGP, resulting in output which looks something like this:
----- BEGIN PGP FOOBAR ----- Version: 2.6.3 Comment: Processed by Mailcrypt 3.5.5, an Emacs/PGP interface ... ----- END PGP FOOBAR -----
To change the comment to one of your own, set the variable
mc-pgp-comment. Set it to nil to use PGP's default, which
is probably either no comment or something defined in `config.txt'.
mc-pgp50-comment and mc-gpg-comment are the corresponding
variables for the other versions.