0x10: Generic certification of a User ID and Public-Key packet.
0x11: Persona certification of a User ID and Public-Key packet.
0x12: Casual certification of a User ID and Public-Key packet.
0x13: Positive certification of a User ID and Public-Key packet.

0x18: Subkey Binding Signature
0x19: Primary Key Binding Signature
0x28: Subkey revocation signature

0x1F: Signature directly on a key
0x20: Key revocation signature
0x30: Certification revocation signature

0x20: Key revocation signature
   The signature is calculated directly on the key being revoked.  A
   revoked key is not to be used.  Only revocation signatures by the
   key being revoked, or by an authorized revocation key, should be
   considered valid revocation signatures.