Pirate's flag (5,5)
I believe the answer is:
jolly roger
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pirate's flag</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for jolly roger that I've seen before include "Pirates' flag" , "Pirate flag" , "standard for boarders?" , "In the main a fearful sight" , "standard not welcomed in the main" .)