It means "municipal police" , city cops
....marked, or more better to say "unit marked" prior to WW2, but most likly saw service in WW2...and I was mistaken, it is weapon 336, not perhaps Luger 336 in stock, but weapon #....listen this is all to confusing, just send me the gun, it would look nice in my collection, and since you did not sell it to me, you could visit it anytime")....hope this helps