For what it's worth (i.e. nothing):

     When I started teaching as an adjunct 13 years ago, I was really
     nervous that no students would take me seriously since I had already
     by confused for a freshman the week class started.  So I made class a
     formal one where I addressed the students, law-school style, as Mr. or
     Ms. So-in-so and asked them to reciprocate.  Then I teasingly told
     them the rules of my grading.

     Call me Dr. Fort and you get an A
     Call me Professor Fort and you get a B
     Call me Mr. Fort and you get a C
     Call me Tim and you get a D
     Call me anything worse than that and you flunk.

     Unfortunately, I found out that several people took me seriously and
     were quite upset.  So now, I just tell them to call me Tim and let it
     go at that.