XO

I always assumed that O was a hug, because it made me think of wrapping my arms around someone, and that X was a kiss by elimination.

X is a kiss because it (vaguely) looks like puckered lips. O is a hug, because it looks (vaguely) like arms encircling ..well.. nothing really, but you get the idea.

XO is also some kind of alcoholic beverage, is it not?

XO means Badtz Maru in Japanese. X means wrong, and is often accompanied by a buzzing sound, even in conversation. O means right and is accompanied by a doorbell sort of sound, which is pronounced "pin-pon!" when people say it.

XO is also the symbol for famous children's cartoon crow Bad Badtz Maru, who is one of Hello Kitty's friends.

An acronym standing for "eXtra Old" qualifying cognac as having aged in oak barrels for at least 6.5 years.
Older and more expensive than VSOP or VO.

In the American (and Canadian: thanks Palpz) Armed Forces, XO is an informal way of addressing a second in command, being an abbreviation of eXecutive Officer