The traditional date of Epiphany is January 6, but in the United States it is celebrated on the Sunday after Christmas, between January 2 and January 8. This year the solemnity is celebrated on Sunday, January 8. The whole of the Christmas season, especially on the feast of the Epiphany, is a traditional time to bless homes, including passageways and doorways.
Often related to these blessings is a ritual of “chalking” the doors of the home with the numbers of the year separated by the initials, CMB. The letters traditionally refer to the legendary names of the three kings: Caspar, Melchior, and Balthasar (Scripture neither names them nor says there were three of them). Another tradition refers to it as the abbreviation of the Latin phrase, Christus mansionem benedicat, translated as “May Christ bless this house.”
To chalk the door for Epiphany, one would write in chalk on the outside lintel above the door: 20 + C + M + B + 12.