A couple of weekends ago I went to Oppenheim I found this formula in several doors around the village. I was so intrigued I had to ask what it was all about. It seems it’s a catholic custom. The “Sternsinger” (star singers) are kids dressed up as the kings from the east (http://en.wikipedia.org/wiki/Biblical_Magi) roaming the towns and villages collecting sweets for themselves and donations (money) for the church.
When those kids visit a house they leave that strange formula written on it. Thanks to Joerg for the explanation ;)