"X" is often used in English to indicate signature lines:
John Q. Sekicho
President and CEO
Sekicho Heavy Industries Co., Ltd.
...as well as kisses.
i miss u hun ok? lots of love xxxxx -pookie
Most people don't know how these practices arose... or that they both come from the same source. Y'see, back in medieval Britain, people would write a St. Andrew's cross after their signatures, to indicate their good faith. After drawing the cross on the document, they would kiss it.

Over the centuries, the cross gradually mutated into an X, and even though people stopped kissing it, they still correlated kisses with X's.

Now you know, and knowing is half the battle...