The file doc/DETAILS says on the format of "Field 11 - Signature class":
This is a 2 digit hexnumber followed by either the letter 'x' for an exportable signature or
the letter 'l' for a local-only signature. The class byte of an revocation key is also given
here, 'x' and 'l' is used the same way.
However, the gnupg source (g10/keylist.c) formats the output by function print_revokers() as follows:
es_fprintf (fp, ":%02x%s:\n", pk->revkey[i].class, (pk->revkey[i].class & 0x40) ? "s" : "");