MB Rostock-apology to Heinz

Dear list and particularly Heinz
I'm sorry if you were offended by my reply to your answer to my query.
I didn't mean to upset anyone, but rather was trying to point out that I
was trying to find a film number for the 1819 census, not the Kessin church
records.
I am currently looking at the church record, but I'm bewildered by this MB
next to the Rostock in the census index.
I can only find RA and Stadt as I said before, and haven't a clue as to
what the MB may mean.
Once again, I'm sorry if I offended anyone.
Regards
Leonie