Crossword Genius

People in line overheard signal for action (3)

Ross

I believe the answer is:

cue

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'signal for action' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for cue that I've seen before include "Actor's line to remind another" , "strike" , "Hint, prompt" , "On a car[D?] this would give a prompt" , "Sign" .)

I've seen this clue in The Independent.
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