The Secret History of a Financial Icon

Several theories exist about the origin of the U.S. dollar sign ($). The most credible is probably that it evolved from Ps, an abbreviation for Spanish pesos, which were widely circulated in colonial America. After the Revolution, the “s” gradually came to be written over the “P” until the combined letters closely resembled the dollar symbol we know today.

Source: U.S. Bureau of Engraving and Printing