The dollar sign ($) is a globally recognized symbol for money, but its exact origin is a surprising historical puzzle.

Key idea: The dollar sign emerged in the 1770s to represent the Spanish American peso, influencing the US dollar, but it took time to appear on currency or in print.

The dollar sign first started showing up in business papers in the 1770s. Back then, it referred to the Spanish American peso, which was also known as the "Spanish dollar" or "piece of eight" in British America. These Spanish coins were very important and became the model for the currency the United States created in 1792.

Even though the US dollar was established, early US dollar coins did not actually have a dollar symbol on them. The first time the '$' sign appeared in print in the US was supposedly in the 1790s. Later, an 1869 US Note even featured a large symbol that looked like a 'U' overlapping an 'S', similar to a single bar dollar sign.

Key idea: The dollar sign likely evolved from either the abbreviation 'ps' for 'pesos' or from the design of the Pillars of Hercules found on Spanish coins.

So, how did a symbol that looks like an 'S' with a line through it come to represent the Spanish American peso? There are a few ideas, and historians are still debating which one is correct.

The most popular idea is that the dollar sign grew out of a shorthand used by scribes for "pesos." In old Spanish American documents from the late 1700s and early 1800s, people would often abbreviate "pesos" as "ps." Over time, the 's' was written directly over the 'p', and these two letters combined started to look a lot like the '$' sign we know today. An Irish trader named Oliver Pollock used this kind of combined "ps" in his letters as early as 1778, which looked almost exactly like the dollar sign.

Another interesting idea connects the symbol to the Pillars of Hercules. These were a classical symbol for the two sides of the Strait of Gibraltar. The Spanish coat of arms showed these pillars with a ribbon wrapped around them in an 'S' shape. This design appeared on many Spanish dollar coins, especially those made in Potosí, Bolivia, which was a huge silver mining center. Some even suggest the symbol came from the Potosí mint's mark, which had the letters "P T S I" layered on top of each other, with the middle looking like a single stroked '$' sign.

“The most popular idea is that the dollar sign grew out of a shorthand used by scribes for "pesos."”

Key idea: Though usually stylistic, the two stroke dollar sign (cifrão) had a specific historical use as a separator in Portuguese currencies and is still used in Cape Verde.

While the one and two stroke versions of the dollar sign are often seen as just different ways to draw the same symbol, there have been times and places where they had specific meanings. For example, the two stroke version (the cifrão) was used in the Portuguese Empire in a special way.

In Portugal and Brazil, the cifrão was used as a thousands separator in their old currency, the real. So, 123500 réis would be written as 123500. Then, when Portugal switched to the escudo, the cifrão became the decimal separator, so 123.50 escudos was written as 12350. This unique use of the cifrão as a decimal separator is still seen today in Cape Verde.

Even though some fonts might show the dollar sign with one or two strokes, computer systems usually treat them as the same symbol. This means that if you type a '$' on your keyboard, it is up to the font you are using to decide if it shows one or two lines. There is no separate computer code for the two different styles.

“In Portugal and Brazil, the cifrão was used as a thousands separator in their old currency, the real.”

Key idea: The dollar sign's inclusion in early computer systems led to its widespread adoption for various non monetary functions in programming and software.

Because the dollar sign was used in early American computer programs, especially for business and accounting, it became a standard character in computer systems. This led to it being used for many purposes that have nothing to do with money in programming languages.

For example, in some programming languages like PHP or Perl, the '$' sign is put in front of a word to show that it is a variable, which is like a placeholder for information. In other languages, it might introduce an expression that needs to be calculated, or mark where text should be inserted. In spreadsheets like Excel, the '$' sign is used to "lock" a cell reference, meaning it will not change even if you copy the formula.

This wide adoption in computing means the dollar sign has a dual life: it is a symbol for money, but also a powerful tool for giving instructions to computers.