Use rel=license

    <a rel="license"
       href="http://creativecommons.org/licenses/by/4.0/">
      <img alt="Creative Commons License" style="border-width:0"
       src="https://i.creativecommons.org/l/by/4.0/88x31.png" />
    </a>
    <br />
      This work is licensed under a
    <a rel="license"
       href="http://creativecommons.org/licenses/by/4.0/">Creative
      Commons Attribution 4.0 International License</a>.
  

Notes

Google uses the rel=license markup, which is included in the Creative Commons recommended markup for their licenses. Using an explicit license makes your content easier to find! Just paste the license from the license selection tool we saw earlier.