Despite being associated with a famous wrestler, a Vin Diesel movie and hardcore pornography, the sign-off ‘xxx’ at the end of a message is ubiquitously and unambiguously used to symbolize a wholesome trio of kisses. In Spanish, however, the letter X is shorthand for ‘por’, meaning ‘for’ or ‘by’, so the link between this versatile character and kissing is clearly not inherent.

Like many cultural oddities, the origins of the use of X’s as kisses are difficult to pin down. According to Dr Laura Wright from the Faculty of English at Cambridge University, the tradition may have something to do with the fact that the Greek letter X is pronounced ‘ks’, which obviously sounds a lot like ‘kiss’.

Yet other researchers favor a different explanation, also beginning with the Greek alphabet. Supposedly, because the Greek word for Christ - Χριστός - begins with an X, the letter itself was previously used to symbolize the Christian faith - hence the continued use of ‘Xmas’ as shorthand for Christmas.

In the Middle Ages, when many people were illiterate, the letter X was often used in lieu of a signature on messages and official documents, signifying a person’s devotion to Christianity. Supposedly, it was also popular to physically kiss the mark once it was made, out of love and loyalty to one’s religion.

Sealing a message (signed X) with a kiss thus became common, cementing the connection between the letter and physical displays of affection. Over time, as the religious connotation faded, the character came to exclusively represent kissing, although exactly when this transition occurred is the subject of debate.

The Oxford English Dictionary, for instance, attributes the first known use of X’s as kisses to a 1763 letter penned by British naturalist Gilbert White, who signed off: “I am, with many a xxxxxxx and many a Pater noster and Ave Maria, Gil White.”

However, given the religious language accompanying the outrageous seven kisses, some scholars have argued that White’s x’s are more likely to have represented holy blessings than smooches.

It’s therefore pretty difficult to say who first ended a communication with kisses, although it seems the slang had become well and truly established by the time Winston Churchill wrote a letter to his mom in 1894, ending with: “Please excuse bad writing as I am in an awful hurry. (Many kisses.) xxx WSC.”