Green’s Dictionary of Slang

a system of telegraphy used on racecourses to keep the bookmakers abreast of the changing odds; thus tick-tack man or ticktacker, one who performs such telegraphy (by using a ‘vocabulary’ of hand and arm movements and signals).

1903		Sun. Times (Perth) 9 Aug. 4/8: And the welshers and the whisperers, the tic-tacs and the tugs.
1929		Hull Dly Mail 17 June 10/2: He called the numbers at rac emeetings [...] He was not a tick-tack man.
1944		Maurer & Baker ‘“Aus.” Rhyming Argot’ in AS XIX:3 195/2: Tick-tack. The Track (racing). Tic-tac, signals to a bookmaker.
1965		F.J. Hardy Yarns of Billy Borker 103: You don’t know what a ticktacker is? Well, I’ll tell you. [...] So Ticktacker Tom would be in the paddock, see, and every time a horse was heavily supported and its price fell, he’d rush over to the fence and signal to Ron, who’d be waiting there. Tom would wave his hands around for all the world like a buyer at a wool sale or a priest giving a blessing at a funeral. That’s what they call ticktacking. Well, these signs would give the number and the odds of the horses.