EmbeddedSignature Signature Subpacket for embedding one Signature into another.

 Exportable Signature Subpacket for marking a signature as exportable or non-exportable.

 Features Signature Subpacket encoding which features are supported by the key-holders implementation.

 IntendedRecipientFingerprint Signature Subpacket containing the fingerprint of the intended recipients primary key.

 IssuerFingerprint Signature Subpacket containing the fingerprint of the issuers signing (sub-) key.

 IssuerKeyId Signature Subpacket containing the key-id of the issuers signing (sub-) key.

 KeyExpirationTime Signature Subpacket containing the number of seconds after the key's creation date, after which the key expires.

 KeyFlags Signature Subpacket encoding the capabilities / intended uses of a key.

 NotationData Signature Subpacket encoding custom notations. Notations are key-value pairs.

 PolicyUrl Signature Subpacket for encoding a URI pointing to a document containing the policy under which the signature was created.

 PreferredAlgorithms Signature Subpacket containing algorithm preferences of the key holder's implementation.

 PrimaryUserId Signature Subpacket marking a User ID as primary.

 RegularExpression Signature Subpacket containing a regular expression limiting the scope of the signature.

 Revocable Signature Subpacket marking a signature as non-revocable.

 SignatureCreationTime Signature Subpacket containing the time at which the signature was created.

 SignatureExpirationTime Signature Subpacket containing the number of seconds after the signatures creation time after which the signature expires.

 SignatureTarget Signature Subpacket containing the hash value of another signature to which this signature applies to.

 SignerUserId Signature Subpacket containing the User ID of the identity as which the issuer created the signature.

 TrustSignature Signature Subpacket encoding the level and amount of trust the issuer places into the certified key or identity.