A Southern custom no one, so far, has been able to explain to me. What are the rules? Why is it done? The custom? Calling adults by Miss or Mister pus their first name. Miss Linda, Mr Billly Bob ... Why? What is the point? When do you use it?
I have come to see it as a stand-offish way to say "Lets pretend we're close but we both know that isn't so.." But, that is probably because I first noticed it as a way the people of different colors talked to each other.
Yes it is a southern thing and a sign of respect for people that too close for the formal Mrs/Mr/Miss Smith yet not a member of the immediate family. I've noticed that black people adhere to it more than whites do.
For example, I have known my daughter's best friend who is 37 since she was about 12. She herself usually calls me mom but her children call me miss sherry. I would rather they call me just sherry but since I understand the why, I deal with it.