Because the dollar sign appeared in ledgers before the United States was a fully formed nation, historians have had to piece together its ancestry through a series of intriguing, if sometimes flawed, hypotheses.

1. The Spanish Pillars of Hercules

One of the most visually compelling theories suggests the symbol is a simplified drawing of the Pillars of Hercules. This image appeared prominently on the Spanish coat of arms and was minted onto Spanish colonial currency. The design featured two vertical pillars entwined with an S-shaped scroll bearing the Latin motto Plus Ultra (“Further Beyond”). Proponents of this theory argue that as merchants and accountants scribbled the image in their ledgers, the two pillars and the winding scroll eventually merged into the “$” we use today.

2. The Potosí Mint Mark

Another theory looks to the heart of the Spanish Empire’s wealth: the Potosí silver mine in modern-day Bolivia. From 1573 to 1825, this mint produced the vast majority of the world’s silver. The mint used a specific mark to identify its coins—a monogram that superimposed the letters P, T, S, and I (for Potosí). When stacked on top of one another, the overlapping letters created a symbol that bears a striking resemblance to the dollar sign, particularly the version with two vertical bars.

3. The “United States” Misconception

Perhaps the most famous theory—and the one most likely to be a myth—is that the symbol is a literal abbreviation for the United States. Under this logic, a capital “U” was superimposed over a capital “S.” Over time, the bottom curve of the “U” was dropped, leaving only the two vertical lines cutting through the “S.”

This theory was famously championed by philosopher Ayn Rand in her 1957 novel Atlas Shrugged, where she framed the symbol as a uniquely American icon of achievement. However, the timeline doesn’t hold up to scrutiny. The symbol appears in documents and trade ledgers well before the name “United States” was officially adopted in 1776; back then, the region was still known as the United Colonies of North America.

The Most Likely Ancestor: The “Peso” Abbreviation

While the theories above are more dramatic, most modern researchers point to a more mundane linguistic evolution: the Spanish “peso de ocho reales” (the Piece of Eight).

In the late 1700s, merchants abbreviated “pesos” as “ps.” As ledger entries were written at high speed, the “s” began to be written directly over the “p.” Eventually, the loop of the “p” disappeared, leaving only the vertical stroke (the “stem”) intersecting with the “s.” This transition is actually visible in the surviving financial documents of Oliver Pollock, an Irish merchant who supported the American Revolution and is often credited with helping popularize the symbol in official government correspondence.

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