Signal that danger has passed (3,5)
I believe the answer is:
all clear
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">signal that danger has passed</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 all clear that I've seen before include "Message confirming safety" , "Encouraging signal" , "Signal that danger is past" , "Signal to resume normal activities" , "without any ambiguity" .)