I know the “!” sticks because of the Akame ga KILL! thread. (lol and this thread too!)
However, the best way to test the “?” (though you’ll have to do this since you’re a Regular) is rename the Invaders of the Rokujyōma!? (Rokujyōma no Shinryakusha!?) thread. Invaders of the Rokujyōma!? (Rokujyōma no Shinryakusha!?)
Just remove the (Rokujyōma no Shinryakusha!?) from the thread title (copy/paste it somewhere before you click the checkmark though, so you add it right back to the title after you test it) and click the checkmark.
-edit-
Though skimming down the Other Anime section, it looks like the “?” sticks too, at least for this thread