Bookies' sign language (3-3)

I believe the answer is:

tic-tac

(Other definitions for tic-tac that I've seen before include "Racecourse bookmakers' telegraphy" , "Racecourse bookmakers' signalling system" , "Bookmaker's arm signals" , "Bookies'' system of arm signals" .)

I've seen this clue in The Sun.

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