The Ithaca HOUR is a local currency used in Ithaca, New York and is the oldest and largest local currency system in the United States that is still operating. One Ithaca HOUR is valued at US$10 and is generally recommended to be used as payment for one hour's work, although the rate is negotiable. HOURS are printed on high-quality paper and use faint graphics that would be difficult to reproduce, and each bill is stamped with a serial number, in order to discourage counterfeiting. More can be found at:
http://en.wikipedia.org/wiki/Ithaca_Hours#Origin