Yes, it's 2A2F, it should be the unicode for the X symbol, and its showing up on top right of the thumbnail. In fact, when I click on this box the app closes.
UPDATE: got the explanation from the dev, it was much more trivial than I thought
. The repos of my distro don't have DejaVu Fonts, so as a temporary workaround I downloaded these fonts from upstream and moved them to a newly created /fonts folder in my home directory.