indexed signature

Definition

Also called siger. An indexed signature attachment is used when signing anything with a multi-key autonomic identifier. The index is included as part of the attachment, so a verifier knows which of the multiple public keys was used to generate a specific signature.
Source:Philip Feairheller

Example working

An indexed signature attachment would look something like:

03.<binary signature>

All encoded as qualified base64. A verifier would then know to use the AID’s public key located at index 3 in the list of public keys to verify the signature.
Source:Philip Feairheller

Witness signatures indexed

In addition, witness signatures can also be attached as indexed signatures. So a verifier can determine which witness signed a particular receipt. This is useful when witnesses are receipting an event and only attaching their own signature. The controller knows which witness signed the receipt by looking up the index in their list of witnesses for that event.
Source:Philip Feairheller