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All answers having "Signals" as clue:

4 Character Answers:

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CUES

QQQQ



5 Character Answers:

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CALLS

HAILS



6 Character Answers:

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ALARMS

ALERTS

LIGHTS

NODSAT



7 Character Answers:

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BECKONS



8 Character Answers:

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GESTURES



9 Character Answers:

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MOTIONSTO