This is from the Catacombs of Priscilla: The three wise men and the Madonna and Christ Child.
I took out the Rituale Romanum on this Feast of the Epiphany from the book shelf in the little chapel of Holy Souls Hermitage and made use of the blessing which recalls Caspar, Melchior and Balthazar, both for the blessing of the clay (chalk) and then the house blessing, with exorcized water/salt.
Oh, and, by the way: I’m sure that the wise men, who are accompanying us throughout 2013, would like us to mediate on two aspects of Christ’s ministry so that we are blessed for the whole year, those being the other aspects of Epiphany which the Church hold’s out to us: the Baptism of Christ (a ferocious mediation on that HERE) and the Wedding of Cana (a ferocious meditation on that HERE). You might want to read those over this week as the Christmas/Epiphany season continues.
Accompany me, Father George David Byers, S.S.L., S.T.D., as I begin life as a Catholic Priest-Hermit by choice. Holy Souls Hermitage is dedicated to the sanctification of my fellow priests, bishops, deacons & seminarians going through the purgatory of this life or the next. Prayer and sacrifice go up, of course, for both Benedict XVI and the next Successor of Saint Peter. 
Your picture reminded me that when I was a litle my parents had our favorite priest bless our house with with chalk and salt and water. 20+C+M+B+13 ? The letters are for Caspar, Melchior and Balthazzar I guess and 20 and 13 is the year. but what is the significance?
We’re asking these wise men, these saints, to come with us throughout 2013, or rather, that in this year, we might accompany them as they adore the Lord in heaven. Yikes! We can do that especially with adoration of the Blessed Sacrament, Jesus, Emmanuel, God-With-Us.
I like that.
When I was married to a Bavarian, we would always visit his mother at this time of year. The Catholic boys would come in robes and write these numbers and letters above the doors. I was pleasantly surprised! I had never heard of such a beautiful and simple ritual to honor Christ. Good for you for making it happen at the Hermitage, Father!
This tradition is still very much alive in Austria (above every door in the village we stayed in) and I have also seen it in some parts of Germany.