Currently the only way to know if you can quit in a specific non-city room is if you try quitting. The problem with this is you will never know of these places unless you're ready to quit and randomly try quitting in various spots. This isn't very practical. How about placing some kind of sign at all the random quit spots? Something like a stone marker or collumn that kind of stands out. I don't think this would be detrimental to the game.

Though I think that the skill should be 100% reliable when telling rooms where you can quit(which it wasn't when I had it).