[baud147258]

As a French, it feels weird to learn something about my language on an English site :|. I don't remember seeing it written in French. Or I saw it, understood the meaning and forgot.

[lloeki]

That's because it's largely unused nowadays, the current abbreviation being MM. (which doubles the M. – not Mr! – abbreviation for monsieur).

[GuiA]

You’ve probably heard it without noticing - eg “Mesdames et messieurs” (ladies and gentlemen) is still in common use.