Since the Middle Ages there has been a tradition that on (or near) the feast of the Epiphany Christians pray for God’s blessing on their homes, marking the entrance with chalk (an ordinary substance put to holy use). The front entrance of the home is marked with the initials of the legendary names of the Magi – Caspar, Melchior, and Balthasar – written between the numerals of the new year. All the symbols are connected with crosses.
Some suggest that the letters C M B may also stand for Christus mansionem benedicat, “May Christ bless this house.”
Following is the Epiphanytide doorway blessing from the book Catholic Household Blessings and Prayers (2012). It's the blessing we used today at Spirit of St. Stephen's.
Welcoming God, bless this door.
May all who come through it find in our home
welcome, love and friendship.
Welcoming God, help us keep the door of our heart open.
Do not let fear, prejudice or hatred lock our door.
May we be hospitable to all as you are.
Welcoming God, bless our comings and our goings.
Teach us not to hurry through life's doorways
lest we miss You who beckon us at the threshold.
Never let us forget that where You are, God,
the door is always open.
See also the previous Wild Reed posts:
What We Can Learn from the Story of the Magi
Feast of the Epiphany
We Three . . . Queens