ISO/IEC 20008-2:2013

ISO/IEC 20008-2:2013 specifies anonymous digital signature mechanisms, in which a verifier makes use of a group public key to verify a digital signature.
It provides

a general description of an anonymous digital signature mechanism using a group public key;
a variety of mechanisms that provide such anonymous digital signatures.

For each mechanism, ISO/IEC 20008-2:2013 specifies

the process for generating group member signature keys and a group public key;
the process for producing signatures;
the process for verifying signatures;
the process for opening signatures (if the mechanism supports opening);
the process for linking signatures (if the mechanism supports linking);
the process for revoking group members.