What does the S in the dollar sign represent?

Cecil replies:

A serpent? Lord, if Florian Cajori were alive to hear such talk, it would just kill him. Professor Cajori dealt with this question definitively more than 60 years ago in A History of Mathematical Notations — not the ideal beach book, maybe, but one I heartily commend nonetheless.

The subject of the dollar sign was close to Professor Cajori’s heart, and he could get quite indignant on the subject. As he tartly noted in his book, “About a dozen different theories [on the dollar sign’s origin] have been advanced by men of imaginative minds, but not one of these would-be historians permitted himself to be hampered by the underlying facts.” Among the deficient hypotheses:

(1) The dollar sign was originally the letters U and S superimposed. The idea here is that the original dollar sign had two vertical lines, not one. Popular though this idea is, there is zero documentary evidence for it. Furthermore, Robert Morris, the Revolutionary War financier and the first U.S. official to use the dollar sign, made it with a single vertical stroke.

(2) It’s a version of the letters IHS, the Greek abbreviation of the name Jesus. No further comment required.

(3) It was originally a P combined with an 8. The dollar, you’ll recall, is descended from the Spanish dollar, also known as the “piece of eight” because it consisted of eight reals. Plausible, and as we shall see not that far from the truth, but still wrong.

(4) The sign was inspired by the Spanish “pillar dollar,” which on one side had two columns signifying the “pillars of Hercules” at Gibraltar. These were represented in the dollar sign by the two vertical lines, with the S being some sort of scroll wrapped around them.

So much for the tomfoolery; now to get serious. Professor Cajori contends that the dollar sign is an abbreviation for “pesos.” Bear in mind that the Spanish dollar, also known as the peso de 8 reales, was the principal coin in circulation in the U.S. up until 1794, when we began minting our own dollars. In handwriting, “pesos” was usually abbreviated lowercase “ps,” with S above and to the right of the P and with the hook on the latter written with one or two deep strokes. As time went on, the P and the S tended to get mashed together and the result was $.

The dollar sign and the PS abbreviation were used interchangeably from around 1775 until the end of the century, after which the latter faded from view. Professor Cajori backs up his argument with examples from manuscript, and I’m prepared to declare the matter settled.

As for the C in the cent sign, it seems safe to say it stands for “cent.” However, you can never be too careful in this business, so I’m continuing to research the question. If there are any further developments, you’ll be the first to know.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.