xo

from my new favourite book, Letter Perfect. The A-Z History of the Alphabet. by David Sacks.

"The custom of writing X's for kisses in signing off a letter dates from the Middle Ages, when much of Europe's population remained illiterate. On legal documents, in lieu of a signature, a person might write an X or the sign of a cross. The signatory would then kiss the X, to promise to stick to the agreement. Over later centuries, the written X came to mean not the signature but the kiss."