Signal that danger has passed (3,5)
I believe the answer is:
all clear
'signal that danger has passed' is the definition.
(I've seen this before)
This is all the clue.
(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" .)