A good notion

Rico says the ladyfriend has long had a mezuzah on the doorpost, and Ann Farmer has an article in The New York Times about others with the same decoration:

The doorways inside 30 Ocean Parkway, an Art Deco building in Windsor Terrace, Brooklyn, are studded with mezuzas of all sizes and styles: plastic, pewter, simple, gaudy, elegant.
The people behind those doors are an assortment, too: Catholics, Baptists, Episcopalians, Buddhists, atheists, and even a few observing the High Holy Days this week.
“I love mine,” said Eva Gasteazoro, a performance artist who discovered a mezuza on the doorway of her second-floor apartment when she moved in ten years ago. Although she was raised Catholic, it never crossed her mind to take down this symbol of a Jewish household.
“It’s a very beautiful one,” she said, running her fingers over the raised Hebrew lettering on its tarnished but ornate metal casing. “A lot of the new ones are plastic,” she added, looking askance at a white mezuza jutting from her Jewish neighbor’s doorway.
Jews have left their mark on every aspect of New York life, but perhaps none are so ubiquitous and tangible as the palm-length encasements attached to countless doorways. So in a city that both savors history and likes to shake things up, it is perhaps inevitable that many of those mezuzas now belong to gentiles.
Left behind when Jewish residents died or moved out, they have survived apartment turnovers, renovations, co-op conversions, paint jobs, and other changes wrought by time.
When Tazio and Todd Hilbert moved into their fifth-floor apartment in Ms. Gasteazoro’s building ten years ago and spotted four mezuzas, Ms. Hilbert said, “We didn’t know what they were.” Although she was brought up Presbyterian and considers herself nonreligious, she kept her mezuza in place. “We never considered taking it down,” she said. “I liked how it was part of the history of the building.”
As any observant mezuza owner knows, they are not only decorative. Each mezuza— the word actually refers to the scroll inside, though most people use it to describe the casing as well— is a tiny parchment inscribed with Hebrew verses from the Torah that include Shema Yisrael, a prayer central to Judaism: Hear, O Israel, the Lord our God, the Lord Is One. The Old Testament commands Jews to inscribe the words “on the doorposts of your house”.
Many Orthodox Jews touch the mezuza upon entering or leaving a home, sometimes accompanying the gesture with a touch to their lips in a simulated kiss.
Traditionally, Jews are expected to affix a mezuza to the right side (when viewed from the outside) of a door frame at approximately shoulder height, tilted inward. Ideally, they should do so upon moving in, but most Jewish authorities allow thirty days because, historically, Jews had to move frequently and under duress and were often unsure where their permanent home would be, said Rabbi Andy Bachman of Congregation Beth Elohim, a Reform synagogue in Park Slope, Brooklyn.
Jewish law commands that every inhabited room have a mezuza on the door, but many Jews in America today put them only on the front door.
Jews leaving a home are expected to leave the mezuzas behind if they believe the next residents will also be Jewish. If not, they must take the mezuza with them, to guard against the possibility that a non-Jew might desecrate it, knowingly or not. If a mezuza becomes too weathered, dirty, or otherwise damaged, it is to be buried, as are all sacred documents, a service that a rabbi or synagogue can facilitate.
Non-Jews, naturally, are not bound by these customs, but many follow them out of deference. Alex Cohen of Borough Park, Brooklyn, who sells, installs and inspects mezuzas under the business name Mezuzah Man, said he had answered calls from non-Jews asking him to remove their mezuzas. The mezuzas should be handled respectfully, he said: “You don’t just put it in the garbage.”
But many gentiles choose to keep their piece of Judaica in place. “It’s good karma, if I can mix my religious metaphors,” said Brian Hallas, a resident of Kensington, Brooklyn, who teaches kindergarten at the Calhoun School in Manhattan. Although his mezuza was heavily camouflaged in what he described as a “lovely institutional beige” hallway tone, he spotted it immediately upon moving in, having once received a mezuza necklace from a college sweetheart. “They took theirs down,” he said, pointing to a neighbor’s doorway, where all that remained of a mezuza was its footprint, stamped in the pea green color of the building’s previous interior.
The prospect of such a paint scar is what kept Eleanor Rodgers from removing the mezuza from the doorway of her home on Albemarle Road in Brooklyn, in a heavily Jewish neighborhood. “We’re not only not Jewish, we dislike organized religion,” said Mrs. Rodgers, a doctor’s receptionist who grew up in Ireland.
The mezuza-owning gentile might not be so unusual in a city where bankers live in artists’ lofts and almost every nationality has a pizza parlor. But the idea does not sit right with some observant Jews who see the mezuza as an important emblem of Jewish identity. “To me, it’s very offensive,” said Sara Sloan, a retired schoolteacher in Windsor Terrace. “It’s taking my custom.”
She has mezuzas on every door frame except those for bathrooms and closets. And if she ever moves out, she will take them with her, unless she is certain the next residents will be Jewish. “I have contempt for people who didn’t care enough or respect tradition enough to remove it,” she said.
Still, Connie Peirce, 87, a retired secretary and Catholic who lives in Peter Cooper Village in Manhattan, said she often wished she had inherited a mezuza like many of her non-Jewish neighbors did. The tradition recalled her youth, she said, when her local priest appeared each Easter to write “God bless this house” on her family’s front door. To her delight, one of her Jewish neighbors recently hung a mezuza on her doorway. “Every time I come home and remember, I kiss it and touch it and then I bless myself, saying, ‘In the name of the Father, the Son and the Holy Spirit, amen.’ ”

Rico says that, not being religious, he doesn't really care one way or another, but it's a nice tradition, so what the hell...