You're right. If they're doing it right, bars won't suggest "angel shots" any more, because abusers recognise that signal too. They'll have their own signals posted on the wall in the women's toilets. The simplest one I've seen is one of those remote doorbell thingies in one cubicle, the idea being you lock yourself in the cubicle, ring the bell, and don't open the door until the bouncer arrives.

That seems plausible.