A white Malta cross on a black background, one of the insignias attributed to the <a href="https://en.wikipedia.org/wiki/Knights_Hospitaller" class="extiw" title="w:Knights Hospitaller">Knights Hospitaller</a>
Own work
Derivative work of public domain image <a href="//commons.wikimedia.org/wiki/File:Maltese-Cross-Heraldry.svg" title="File:Maltese-Cross-Heraldry.svg">File:Maltese-Cross-Heraldry.svg</a>