That's our front door with its chalk blessing for 2020. This is an old Epiphany tradition. The C, M and B represent the traditional (not biblical) names of the wise men who followed the star (Caspar, Melchior and Balthazar). Helpfully the initials can also represent Christus Mansionem Benedicat (Christ bless this house). This is such an easy thing to do with children. Chalk the door (or the lintel, or the walls of the house) and say a short prayer of blessing on the home for the coming year. And every time you come home, you have a reminder of Christ's blessing.