Zero Hex said
So how exactly does a cell of assasins operate by wearing highly distinguishable masks that mark them as members to anyone who sees them? Or is the whole "don't reveal your face" thing reserved only for missions and Brotherhood gatherings? 'cause otherwise it seems rather counterproductive, members might as well wear a big bright sign branding them as a target.
It has to do with the God of Misfortune, even though some characters aren't religious the Gods in term do "exist" and by taking off your mask it is punishable by the God of Misfortune. They're basically bound by their masks for the cause. The Mad kingdom is a kingdom of the night. The Brotherhood takes the shadows at night but during the day they are free due to the kingdom being inactive. Most if not all Brotherhood members know the risks they are taking by being part of this. The one's who take it lightly are most likely dead. By joining the Brotherhood you have given something up to show you mean it with your life.
Basically you have given up your true self to become a follower of the God of Misfortune. Which doesn't mean you've forfeit your faith of the other gods.
If my information is not correct PlainFoxxy will call me out on it and fix it. But I do hope this helps answer your question.