Epiphany. The Day of the Three Kings is always on January 6 and the day is a holiday in Bavaria.
Children dress up as the three kings who visited Jesus in the manger in Bethlehem. The kids knock on doors and offer to write a symbol of blessing over the top of people's entry-way doors. In exchange, the “blesee” is expected to give a donation to the Sternsinger, an organization that does various charitable works around the world. The Motto of this year's Sternsinger action is "Gesunde Ernährung für Kinder auf den Philippinen und weltweit!" - Healthy nutrition for children in the Philippines and around the world.
The formula is quite simple: the 20 and the 15 on either end signify the current year. Ihave heard two storied about the meaning of C+M+B and have had locals get vehement about my telling the "wrong" story. One version is that it stands for the names of the 3 wise men, Kaspar, Melchior, and Balthasar. However, Caspar in German is spelled with a "K", so I don't personally like this version of the explanation. The second story is that the C M B stands for the latin, “Christus Mansionem Benedicat” – basically, God Bless this House.