There is a long-standing Epiphany tradition of marking churches, homes, schools, and other buildings with a special 'holy formula' over the entryway with chalk. This formula includes the current year along with the initials C, M, and B in the order shown below.

20 + C + M + B + 18 

The C, M, and B are placed in between the numbers of the current year, with crosses in between each symbol. The three letters have two significations: the invocation Christus Mansionem Benedicat (Christ bless this house), as well as the first initial of the names of the three Magi: Caspar, Melchior, and Balthazar.

Click here to go to the website of the United States Conference of Catholic Bishops for the blessing of the Home and Household on Epiphany.