Why do X's at the end of a letter signify kisses?
In the Middle Ages, when many people were unable to read or write,
documents were often signed using an X. Kissing the X represented an
oath to fulfill obligations specified in the document. Some historians
believe that originally the signature was a cross, changed to an X
which symbolized Christ (Xmas), and represented a gesture of good
faith, like kissing the cross on a Bible. The X and the kiss
eventually became synonymous. Later people thought that the X
symbolized two pair of lips kissing – each half of the X represents a
pair of lips which were facing each other. It marked where the writer
kissed the letter, so that the receiver could kiss the same spot.
Happy Valentine's Day!