This is gonna be a short thread. Once I have the answer there's not much to discuss. Couldn't find the answer online, so I'm trying here.
I've been re-reading Jules Verne's 20,000 Leagues after many years. The protagonist (or maybe I should say co-protagonist) is one Pierre Aronnax, a French professor who gets picked up by Captain Nemo's sub and taken for a ride. During conversations, as written in the spoken dialogs, Aronnax is addressed thusly:
"I will show you the wonders of the oceans, M. Aronnax," said Nemo.
Now I know the "M." is like "Mr." and stands for "Monsieur" but what I don't know is if in spoken French Nemo would just be saying "M" or pronouncing the entire "monsieur." I mean, in English we don't say "M-R" but pronounce the word "mister," so I suspect the latter. But as I read these dialogs I find myself saying the "M" in my head as I read. Never having studied the French language, I have a hard time replacing "M" with "Monsieur." But that's gotta be right, right?
M. would be read/said Monsieur, Mme Madame, and Mlle Mademoiselle. No one would ever try to pronounce the abbreviation, even the single letter.
Since Jules Verne was French, I assume the story was originally published in French and there used the normal conventions for representing abbreviations in speech. The decision to leave the honorific M. untranslated in the English version should really be attributed to the translator.
Heimhenge said
This is gonna be a short thread. Once I have the answer there's not much to discuss.
You really think that is true with this group. 
tromboniator said
M. would be read/said Monsieur, Mme Madame, and Mlle Mademoiselle.
So, is there a French equivalent of Ms.-- Mizz?
Mrs stands for "mistress", which, at one time, was a respectful term for a man's wife.
What was the timing and the driving force that led wives to be called "missuz" and led the word "mistress" to be reserved for unmarried "kept women"? Was this a result of the suffragette movement?
A young man is sometimes called "master". Does a master become a mister when he gets married (that is, a mister has a mistress) or when he becomes self-supporting, or when he becomes legally responsible for his obligations? Or is it when he completes his training and moves from apprentice to master of his trade?
Although I remember the coining of the Ms. title, I'd have to do some research to figure out when it happened. Sometimes, it's easier to remember history if you didn't experience it too closely.