What's the reasoning behind abbreviating hugs and kisses as X's and O's? Some say X is for hugs and O is for kisses, and some say the other way around; but why X and O, and why are they doubled?
X is for kisses, and O is for hugs.
Simply, the X symbolizes the lips being in "kissing" position, and the O are the arms "hugging" seen from above.
Imagine watching 2 people hugging each other from above, you'd see 2 half-circles crossing each other, so more or less a "O".
See also this: What is the origin of "xox"?