It is an ancient custom for Christians, at the season of Epiphany, to write beside the front door of the house the traditional names of the Three Wise Men: KASPAR MELCHIOR & BALTHASAR or just to write their initials, thus: K+M+B and to add the date of the current year.
This shows our willingness to offer hospitality and shelter to the Magi on their journey to Bethlehem: this, of course, means that we are willing to receive all who love and seek our Lord Jesus Christ.
The chalk is first blessed by the Priest during Mass on the feast of the Epiphany.
The prayer said at the Blessing of Chalk:
The Lord be with you.
And also with you.
LORD God, you have given us all we need for soul and body: we thank you for this chalk which you have created for our use. We ask you to bless these + pieces of chalk. May we who take them to write beside the doors of our homes the names of your holy wise men KASPAR, MELCHIOR, and BALTHASAR, be helped by their prayers and come to share in their reward. So may our bodies be healthy, and our souls be saved.
We ask this though Christ the Lord. Amen.
The chalk is then sprinkled with holy water.