Originally, the parish priest would visit each home and write above the door with a piece of chalk. This is hardly practical in larger cities. In our parish, those who attend mass that day can take home with them a small adhesive banner with a gold inscription: 20+C+M+B+20. The numbers refer to the year and the letters CMB stand for Christus Mansionem Benedicat - Christ Bless this Home. Fasten it above the door, either inside or out.