I thought this would be a fun subject to investigate, espceially since the Federal Reserve is considering raising interest rates.
Our dollar sign most likely dates back to 15-century Spain. When King Ferdinand II of Aragon took Spain from the Moors in 1492, he added two ornate columns to his coat of arms because he also claimed the Strait of Gibraltar in addition to the Iberian Peninsula — the mythological Pillars of Hercules being the Rock of Gibraltar and Jebel Musa in Africa. Ferdinands’s heraldic pillars also had a ribbon around them with the Latin words plus ultra, or “further beyond”, recognizing Columbus’s discovery of the New World in that same year. As gold and silver were shipped to Spain from the New World, newly minted coins were stamped with the two pillars and the entwined ribbon. Over time, the symbol became especially associated with the Spanish peso. The U.S. dollar copied the peso’s weight and value, and thus the symbol. In time, the two lines became one, although two lines are still occasionally used.
Source: An Uncommon History of Common Things, by Bethanne Patrick and John Thompson, National Geographic Society, 2009, p 113.