In Hyperledger Fabric, signature policies specify the identities of specific users who must sign a transaction for it to be considered valid. These policies define the endorsement rules associated with a chaincode and are a critical component of the transaction flow. They ensure that transactions are endorsed by the correct entities as stipulated by the governance of the network. Signature policies are not related to the number of nodes, private keys of participants, or the type of consensus algorithm used but are strictly about defining which users or member organizations' signatures are required to fulfill transaction criteria​​.