A black flag.
<a href="//commons.wikimedia.org/wiki/User:Rocket000" title="User:Rocket000">Rocket000</a>
Based on <a href="//commons.wikimedia.org/wiki/File:Red_flag_waving.svg" title="File:Red flag waving.svg">Image:Red flag waving.svg</a> by <a href="//commons.wikimedia.org/wiki/User:Wereon" title="User:Wereon">Wereon</a>. Original PNG by <a href="https://en.wikipedia.org/wiki/User:Nikodemos" class="extiw" title="en:User:Nikodemos">Nikodemos</a>.