Ciao The context is non-verbal communication and its variety of forms. Among others there are: [...] formalized systems of gestures devised for situations in which people cannot usually be heard, such as hand signals for scuba divers or the “tic-tac” system used by bookmakers on racecourses. [...] I'd like to know something more about "tic-tac system" before translating in order to add a few more words to explain what it is. Googling I found it's a question/answer code: is it popular among bookmakers? Among american ones or worldwide? Does an average english mothertongue know what a tic-tac system is? Thanks in advance! W.