docs: def signatures(self, transaction):
          """Sign a transaction.
  
          Args:
            transaction (coinop.Transaction)
  
          Returns:
            A list of signature dicts of the form
              [ {'primary': 'base58signaturestring'},
                ... ]
          """
          # TODO: output.metadata['type']['change']
          if not self.multi_wallet:
              raise DecryptionError("This wallet must be unlocked with "
                                    "wallet.unlock(passphrase)")
  
          return self.multi_wallet.signatures(transaction)