(in the UK) a kind of manual semaphore used by racecourse bookmakers to exchange information.
（英国）（赛马时赌注登记经纪人之间用手表示的）秘密信号
Origin
Mid 16th century (denoting a repeated ticking sound): imitative; compare with tick-tock. The current usage (originally slang) dates from the late 19th century.