I worked in bars in San Francisco's Castro district from about 1989 - 1996 and we had a similar program - we didn't use the name Angela but we had a different name every day as a signal that someone needed help. These were unusual (for the time and place) but not outrageous names, and of course we wouldn't use the name of a staff member or "regular" patron. Some of the names I remember are Maeve, Oksana, Rhonda, and Shoshana.
The name would be posted in the "ladies' room" (toilet) and at the time, it was not acceptable for men to access that room. The person that needed help would approach the bar and say something like "Is Maeve working tonight?" and the staff member approached would take it from there. Everyone was trained to do this and everyone knew the name of the day.
If someone did ask, usually we tried to get the person asking into a private space and find out what she needed, but if that was not possible we could at least keep an eye out and involve our security staff and even the local police if needed/requested.
I'm wondering now if we should have had something for men who felt in danger but - despite the bars I worked in being very gay-friendly, and in one case gay owned - I can't remember that topic ever coming up.