Despite its historical importance and ubiquitous usage, the original meaning of the United States dollar sign ($ or ) remains a subject of debate. Various competing theories exist to explain the origin of this symbol, some tracing its lineage to long before the Revolutionary War.

According to the Oxford English Dictionary, the symbol as we now know it “first occurs in the 1770s, appearing in manuscript documents of English-Americans who had business dealings with Spanish-Americans.” It then “starts to appear in print after 1800” (though according to a plaque in Scotland it was cast in type as early as 1797).

The symbol began to see usage in official government documents in the years that followed. But despite its critical importance to the monetary system of a growing nation, there is no known record of anyone explicitly designing this symbol from scratch.

Pieces of Eight

Many sources, including the OED, assert that the symbol evolved from an abbreviation of peso. The “peso de ocho reales” (or “piece of eight”) was often shortened to Pˢ (a P with a superscript S). At the time, this was a common currency used in the Americas and internationally — in fact, it was legal tender in the United States up through 1857. Going by this explanation: as the P merged into the S, the vertical line persisted and curve was dropped. But this is not the only possible origin story.

Pillars of Hercules

Another hypothesis traces the symbol’s origins to the Pillars of Hercules, featured on Spanish coats of arms and national currency (below). On coins of the period, the pillars were wrapped in S-shaped banners. Per this theory, these could have evolved in notation to become the familiar single-stroke variant ($). The pillars themselves also have a curious history, wrapped up in Spanish colonialism.

The Pillars of Hercules were said to symbolize the end of the known world, flanking the Strait of Gibraltar as a warning to sailors — and, according to legend, a motto was inscribed on them: Non plus ultra meaning “nothing further beyond.” In the 1400s, Ferdinand II of Aragon adopted the symbol of the pillars along with their Latin warning.

After Christopher Columbus came to America, though, the motto was changed to Plus ultra, meaning “further beyond.” The pillars and banner became a symbol of the New World. One can see hints of the single-stroke dollar symbol in minted coinage of the period — the right pillar in the coin above does look like an S wrapping a vertical line.

United States or Units of Silver

Presumed to be a false etymology at this point, a nonetheless fascinating alternative was postulated by a university professor in the late 1800s: the double-lined version of the dollar sign could be a simplified expression of U.S. (the U and the S merged and the bottom portion of the U dropped). This unlikely narrative appeals to some, presumably, because it would make the design uniquely American.

It’s also possible that the symbol indeed combined a U and an S, but that these stood for ‘Units of Silver’ rather than United States.

Thalers and Sense

The sign’s origins aside, the word “dollar” traces back to the Thaler, a silver coin minted back in early 1500s Bohemia. Few ideas, names or designs, as it turns out, are truly original to any one place.

Meanwhile, for those interested in diving deeper into the debate, check out the Wikipedia Talk Page behind the “Dollar Sign” entry.

Special thanks to Nathan Quinn, the 99pi listener who suggested we cover this subject. He also points out there are historical precedents for inserting the dollar sign into a person’s name (à la Ke$ha), with Ambrose Bierce calling Leland Stanford names like ‘Stealand Landford’ & ‘£eland $tanford’.