Chalking the door is one of the Christian Epiphanytide traditions used to bless one's home.[1]
Either on Twelfth Night (5 January), the twelfth day of Christmastide and eve of the feast of the Epiphany, or on Epiphany Day (6 January) itself, many Christians ... write on their doors or lintels with chalk in a pattern such as "20 ✝ C ✝ M ✝ B ✝ 23". The numbers in this example refer to the calendar year 2023 and the crosses to Christ. The letters C, M, and B stand for the traditional names of the Magi (Caspar, Melchior and Balthazar), or alternatively for the Latin blessing Christus mansionem benedicat ('May Christ bless this house').[2] Another form, for Three Kings day, is to mark the door with "IIIK" (the Roman numeral three followed by "K" for "Kings").
Chalking the door is done most commonly on Epiphany Day itself. However, it can be done on any day of the Epiphany season.[3] In some localities, the chalk used to write the Epiphanytide pattern is blessed by a Christian priest ... on Epiphany Day, then taken home to write the pattern.[4]
The Christian custom of chalking the door has a biblical precedent as the Israelites in the Old Testament marked their doors in order to be saved from death ... Families also perform this act to represent the hospitality of the Holy Family to the Magi (and all Gentiles); it thus serves as a house blessing to invite the presence of God in one's home.[6][a]
via Wiki
It's quite common here in Germany.
The local Catholic Church comes around and marks the lintel with the year and K ✝ M ✝ B (K is for Kaspar rather than Caspar).
Where I live is more Evangelical than Catholic so there are fewer doors marked, but not too far North of here it's much more Catholic so you see a lot more doors marked like that.
There's also another custom for January 6th/Epiphany where a coin or some other item (we use an old ring) is baked inside a cake and the person that finds it is, "King for the day."
Interesting...I had never heard of this tradition...thanks.
Never heard of this, but my pastor said that we could bless our homes with 'oil' such as olive oil by marking above both doors and sides. This is in resemblance of the Israelites marking theirs with lamb's blood.