When you flip a coin, the back is upside down in relation to the front.
Not even the U.S. Mint seems to know why that is.
“All U.S. coinage is produced with what is commonly called a “coin turn”, says their Web page.
“That means that the reverse side (tails) of the coins is upside down to the obverse side (heads).
While we have researched the history of this practice, we have been unable to determine the exact reasons.
The Mint still produces U.S. coinage in this manner for traditional reasons and not due to any legal requirement.”
For more facts about coins, as well as some money-themed screen-savers, check out the U.S. Mint’s website: http://www.usmint.gov/