If you think back to Classic, remembe mages got a gaudy tower, whereas the warlocks lept themselves hidden in the basement of a seedy bar.
So in a more realistic setting, as long as they don’t wear signs around their necks, or do someting as stupid as parade their demons on the streets in broad daylight, warlocks can easily keep themselves hidden in plain sight.
Maybe they don’t HAVE patron saints, maybe they make their bargains with pact powers just as described in the 5E book.
Think outside of the MMO box.