I heard that it is not appropriate to call women or girls "小姐" in northern China. That it is considered rough and has a meaning close to "hooker".
So I never address girls or women as "小姐" in the north and even when I am in Shanghai or even further south.
But is it really an issue? And if it is, what should I use instead? Right now I always use 姐 or 大姐 just to be sure I don't "hurt" someone.