The <a rel="nofollow" class="external text" href="https://creativecommons.org/licenses/zero/1.0/">CC-zero</a> icon in black with a transparent background.
Creative Commons (modifications: transparency &amp; slight path simplification)
between 2008 and 2009 <div style="display: none;">date QS:P,+2008-00-00T00:00:00Z/8,P1319,+2008-00-00T00:00:00Z/9,P1326,+2009-00-00T00:00:00Z/9</div>
<a rel="nofollow" class="external text" href="https://creativecommons.org/about/downloads">Downloads - Creative Commons</a> ("All Icons Zip" svg download)