[david_shaw]

> My worry would be that as the signal becomes well known abusers will learn it

I'm so glad that the signal worked in this case, but you're absolutely correct: the problem with clandestine signals like this is that they need to be somewhat widely known to be effective, but if they become too widely known they become ineffective and even dangerous (since the bad actor would likely know the signal and intent).

I've heard stories about prevented tragedies via "code word" drink orders at bars -- maybe that tactic could be more widely applied (bars, restaurants, hotels, gas stations, etc.)

Source (as an example): https://twitter.com/iizzzzzi/status/788387942242914305