The "malplena" symbol, used to show <a href="https://en.wikipedia.org/wiki/Arabic_diacritics" class="extiw" title="w:Arabic diacritics">Arabic diacritics</a> as e.g. the <a href="https://en.wikipedia.org/wiki/Shadda" class="extiw" title="w:Shadda">Shadda</a> or <a href="https://en.wikipedia.org/wiki/Tashdid" class="extiw" title="w:Tashdid">Tashdid</a> ّ
<a href="//commons.wikimedia.org/wiki/User:Shibo77" title="User:Shibo77">Shibo77</a>
<span class="int-own-work" lang="en">Own work</span>