Hugs and kisses

Hugs and kisses or xoxo is a term used for expressing sincerity, faith, love, or good friendship at the end of a written letter, email or SMS text message. There is controversy as to which letter ('O' or 'X') represents which action ('hug' or 'kiss').

Origins
The common custom of placing "X" on envelopes, notes and at the bottom of letters to mean kisses dates back to the Middle Ages, when a Christian cross was drawn on documents or letters to mean sincerity, faith, and honesty. A kiss was then placed upon the cross, by the signer as a display of their sworn oath. It was also used in early Christian history as much of a display of the same.

Since most of the common people could not read or write, the 'X' was placed on documents, and a kiss was placed over it as a show of their sincerity. The Chi Rho, often represented with the letter 'X', was also used as a holy symbol throughout Christian history as it represented the Greek word for Christ ΧΡΙΣΤΟΣ; this gave rise to the practice of using the letter 'X', which was then kissed in this tradition of displaying a sacred oath. (Incidentally, the pronunciation of the letter "X" in Spanish, though generally transliterated as equis, does sound like a native Spanish speaker saying "a kiss" in English.)

There is speculation on the internet from at least one original source, that the 'O' is of North American descent: when arriving in the United States, Jewish immigrants, most of whose first language was Yiddish, would use an 'O' to sign documents, thus not using the sign of the cross, and shop keepers would often use an 'O' when signing documents, in place of an 'X'.