(RNS) When I was a young girl, my mother taught me to add “x” and “o” — a kiss and a hug — after my signature. So deeply embedded was this English-language tradition that it never crossed her mind that these symbols had anything to do with religion. I never thought about it myself until she passed away a few years ago and I found myself emitting streams of “x’s” and “o’s” like a binary love code in the countless emails that consume much of my daily life. From where do these emoticons that English speakers of all faiths sprinkle so liberally come? Let’s start with the “x” — a simple, easily drawn shape that got its start in Western civilization as the ancient Phoenician letter “samekh” for the consonant sound “s.” In early Hebrew, “x” was the letter “taw” and makes an appearance in the Book of Ezekiel as a mark set “upon the foreheads” to distinguish the good men of Jerusalem from the bad. With the advent of Christianity, “x” came to stand for Christ. “In Christian texts, one abbreviation of the Greek christos — meaning messiah — used the first two Greek letters of christos, chi (X) and rho (P), combined into one shape,” says Stephen Goranson, a historian of religion at Duke University who studies the etymology of symbols and words. “So both orientations of crossed lines — the ‘x’ shape and the more-or-less lower case ‘t’ shape — took on religious significance among Christians.” Once it was a sacred symbol, the “x” represented “faith and fidelity,” says Marcel Danesi, a professor of linguistic anthropology and semiotics at the University of Toronto. It became the signature of choice in the Middle Ages, when few could write and documents were sealed with an x embossed in wax or lead. This may be when the “x” first became associated with the kiss: It was customary to close books with a kiss, and oaths of fealty to kings were sealed with a kiss. “Symbols have a way of jumping from one domain to another, and it’s a small step to come from sealing a letter to sealing a love affair,” says Danesi, who wrote “The History of the Kiss: The Birth of Popular Culture.” He speculates that “x” underwent a conversion in an act of medieval romantic rebellion. “Romantic love becomes an obsession, and the kiss became empowering.” This may have been particularly true for women, who had less say than men over the choice of lovers. “The kiss became ‘If I kiss that man, then this is the man I love and want,’” says Danesi. “So much was packed into that symbol of a kiss. … It has become a kind of collective memory. We use ‘x,’ even if we don’t know why.” There’s another theory about how “x” crossed over into kissing territory. According to Goranson, “x” was a symbol for a blessing, and blessings and kisses have long been intertwined in the human psyche. “Mystics went back and forth on the love of God and love of a beloved spouse going way back,” he says. “Just look at The Song of Songs. The same song could be one person’s devotional hymn and another’s love poem.” “A Woman of Valor,” the Hebrew poem recited by Jewish husbands to their wives before the Sabbath evening meal, is also understood to be an expression of love of God. When the circle — “o” — came to signify a hug is another unknown. I stumbled across an unexpected Jewish angle postulated by the late Leo Rosten in his 1968 book, “The Joys of Yiddish.” Rosten suggests that the “o” evolved in connection with the word “kike.” Jews refused to sign entry forms at Ellis Island with the customary “x,” which they interpreted as a crucifix and a symbol of oppression. Instead, they drew a circle, leading immigration inspectors to call Jews “kikel” (or “circle” in Yiddish) or “kikeleh” (“little circle”), which was shortened to “kike.” Most scholars consider this theory apocryphal. Linguist Ben Zimmer says it is far more likely that the “o” stems from an entirely nonreligious source: the ancient Egyptian-Roman game of tic-tac-toe. The game was originally played with pebbles or coins and only incorporated the easy-to-master symbols of the “x” and “o” when paper became plentiful. Zimmer also believes this explains why “x” and “o” are used together. Despite their relatively recent appearance on Valentine’s Day cards, the “x” long ago shed its religious significance, and the “o” likely never had one. And so I — an editor of a Jewish magazine — plan to continue signing off with hugs and kisses. XO! (Nadine Epstein is the editor of Moment Magazine.)