Transparent <b>cc-sa</b>, a <a href="https://en.wikipedia.org/wiki/Creative_Commons" class="extiw" title="w:Creative Commons">Creative Commons</a> <b>Share alike</b> icon:
 "You allow others to distribute derivative works only under a license identical to the license that governs your work."
<a rel="nofollow" class="external text" href="https://creativecommons.org/learn/licenses/">Creative Commons</a>
April 2006 (upload date)
Creative Commons website