A blue X
<a href="//commons.wikimedia.org/wiki/User:Alvaro_qc" title="User:Alvaro qc">Alvaro qc</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>, based on <a href="//commons.wikimedia.org/wiki/File:Nuvola_apps_error.png" title="File:Nuvola apps error.png">Nuvola apps error.png</a>