A gesture of approval (6-2)

I believe the answer is:

thumbs-up

(Other definitions for thumbs-up that I've seen before include "Indication of approval" , "Digital sign of approval as in Roman Colosseum" , "Manual indicator of victory or approval" , "Old Roman sign for mercy, with elevated digits" , "Elevated digits as sign of approval" .)

I've seen this clue in the Sydney Morning Herald.

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