Many houses in Germany has some kind of numbers and letter over the door. It is an annual bendition for the house. The two first, and two last numbers means the year for the bendition. The letters menas C=Christus, M=mansionem B=bendicat (Christ bless this house). But also the letters means C=Caspar M=Melchior B=Balthasar, So the house will be blessed with many gifts from the Three Wise Men.