It's a tricky letter. Not that it's hard to write, but those two lines crossed over one another symmertically has been an over developed symbol for centuries.
I mean: "Sign on the X"
"X marks the Spot"
This symbol has been used for centuries, since people started writing letters with feathered plumes in their hats and an ink well in their desk. This little symbol is known everywhere as a way to show a physical action upon a piece of paper: xxx
Kisses, there in black and white.
How can the be misconstrued?
The four X's is not a symbol of friendship, just like "you will pay" written in blood stained letters on our wall is a little more than a subtle warning of revenge. So the incorrect response to these X's is the "I love our friendship". Especially if you are the person who sent the X's in the first place. Excuse me, but sending xxx is more than just the porn section in the video store! So, if you aren't sure, don't send the xxx's. It's a symbol of affection, is you have no affection then don't mark the spot!