1) Fold a $20 bill in half...
2) Fold again, taking care to fold it exactly as below

3) Fold the other end, exactly as before
4) Now, simply turn it over...
COINCIDENCE?
As if that wasn't enough. Here is what you've seen... 
Firstly The Pentagon on fire...
Then The Twin Towers.
..And now .. look at this!

Last but not least,
911 and the US$20 note
9 + 11 = 20
 
Okay all ripped from email.