Check out some fun facts about the U.S. Dollar and past U.S. paper currency.

The origin of the nickname "greenbacks."
The nickname "greenback" originated as a name for Demand Notes, non-interest notes with green backs issued by the United States in 1861 to finance the Civil War.

Super-sized "money belt"
The 8 billion U.S. notes printed each year are enough to wrap around the earth?s equator over 30 times.

Mile-high millions
A stack of currency 1 mile high would contain over 14? million notes.

In for a pound!
The approximate weight of a currency note, regardless of denomination, is 1 gram. There are 454 grams in a pound, so one pound of currency would contain 454 notes.

Tough stuff!
You would have to double-fold a U.S. currency note about 4,000 times before it would tear.

Woman whose portrait has appeared on U.S. paper currency.
Martha Washington is the only woman whose portrait has appeared on U.S. paper currency. It appeared on $1 Silver Certificates, Series 1886, 1891, and 1896.

"In God We Trust" & U.S. money.
This inscription first appeared on U.S. coins in 1864. Almost a century later, Congress made it the official National Motto, and today its use is required by law on both U.S. coins and paper currency. Use of the motto has been challenged in court many times over the years but has been consistently upheld by the various courts, including the U.S. Supreme Court as recently as 1977.

The origin of the $ sign.
The origin of the "$" sign has been variously accounted for. Perhaps the most widely accepted explanation is that it is the result of the evolution of the Mexican or Spanish "P's" for pesos, or piastres, or pieces of eight. This theory, derived from a study of old manuscripts, explains that the "S," gradually came to be written over the "P," developing a close equivalent to the "$" mark. It was widely used before the adoption of the United States dollar in 1785.