Dear MKE,
Actually, I want to thank you for starting this thread and bringing up these fascinating questions.
I grew up in a house formerly owned by a Jewish family that had mezzuzahs on all the doorways and my parents left them alone. This Jewish family, I should add, also displayed an icon of the Mother of God . . .
Lemko raised the intriguing point about the Portal Icon of the Mother of God and there certainly is a Jewish connection here.
Our Jewish brothers and sisters have what they call a "Mizrah" frame, a framed picture of Jerusalem or another them that is placed in the Eastern corner of the home so that they will always know to face East when praying as a family. This is like our icon corner . . .
When Jews entered or left their homes, they would touch the mezzuzah and pray the Shema. As Lemko notes, we of the East also pray before and after entering our homes and Churches - at the door, I mean.
St Alphonsus Liguori notes the practice once prevalent in the West of saying a Hail Mary before and after entering a home, and then kissing the shrine of the Virgin Mary that should be somewhere in the doorway.
The portal icon or any icon for that matter should be in our doorway so that we can say the "Entrance and Departure Bows" and the Old Believers have a very developed ritual here.
They make the Sign of the Cross with three metanias or bows to the waste before their portal icon saying the Prayer of the Publican. Then they say the prayer "It is truly Meet" to the MOther of God and make a bow to the floor - using a pillow so as not to soil the hands.
Then the Glory be with three more bows to the waste ending with the praying:
Lord Jesus Christ, Son of God, by the prayers of Thy Most Pure Mothers, the protection of Thy Precious and Life-Giving Cross, the intercession of my Holy Guardian Angel (one's Patron Name-Saint, the Saints of the day) and all Thy Saints, have mercy and save me a sinner, for Thou art Good and a Lover of Mankind. Amen.
And this ends with another bow to the ground. These prayers are said in the doorway, coming and leaving house, Church and other people's homes and when entering and leaving a cemetery.
The Oriental Christians, especially the Ethiopians who have a very full measure of Judaism in their liturgical practice, do reverence and kiss the doorposts of their churches as they enter in, and actually say the Shema, as did, at one time, the Celtic Christian monks.
When a priest blesses a home in our tradition, he will walk around making Crosses on the doorposts and also throughout the house.
I have a small altar stand at home and I love walking around it, reverencing its four corners the "horns of the altar."
I think that's rather, well, neat!
I've also taken to wearing the Ethiopian prayer shawl, that looks like a Jewish prayer shawl, except with crosses . . .
Do you think I need help?
Alex