Certain fire sign (3)
I believe the answer is:
leo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">certain fire sign</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for leo that I've seen before include "sign of summer" , "Name taken by 13 popes, the last dying in 1903 aged 93" , "one of several popes" , "Fifth sign of the zodiac" , "Man" .)