<ds:SignatureProperties xmlns:ds="http://www.w3.org/2000/09/xmldsig#" Id="def456">
  <ds:SignatureProperty Target="https://simplesamlphp.org/some/target" Id="abc123">
    <ssp:HSMSerialNumber xmlns:ssp="urn:x-simplesamlphp:namespace">1234567890</ssp:HSMSerialNumber>
  </ds:SignatureProperty>
</ds:SignatureProperties>