code: func (c *Client) SignerPublicKeyBlobref() blob.Ref {
  	c.initSignerPublicKeyBlobrefOnce.Do(c.initSignerPublicKeyBlobref)
  	return c.signerPublicKeyRef
  }
docs: // SignerPublicKeyBlobref returns the blobref of signer's public key.
  // The blobref may not be valid (zero blob.Ref) if e.g the configuration
  // is invalid or incomplete.