The Origins of
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The US theory: Several people have suggested that the US symbol came from the use of a S stamped over the top of a U as a symbol for the United States. The theory has even been cited in newspapers and encylopedias. Not only is there no documentation to support this origin, but as Cajori points out, it flies in the face of the earliest recorded usage of the dollar symbol by a high US official. In an exchange between financier and statesman Robert Morris and his secretary in 1792 show a use of the symbol with only a signel vertical stroke. In the earliest period of usage of the symbol it would seem unusual that a man highly involved in the US financial operations did not know of its true origin.
The Portugese Thousand For a time both the Spanish and the Portugese used a symbol somewhat simiar to the dollar symbol that represented thousands. The Spanish term was calderon and used a symbol similar to a U, but the Portugese used a symbol very nearly like the present $, called a cifrado. In the 1500's the use of Roman Numerals and Arabic numerals were both still common, and the number 12,410 might have been written in Portugese as XII $ CDX with Roman letters, and the cifrado representing "times 1000". It was also used in Arabic numerals and the same value might have looked like 12 $ 410. While this is a likely candidate, there is no evidence of it changing meaning and migrating to the front of the number in any of the Nations that used either Spanish or Portugese (or anywhere else, it seems).
The Pillar Dollar The two promentories on either side of the Straights of Gibralter are often called the Pillars of Hercules. In mythology it was Hercules who supposedly raised the Rock of Gibralter on the European side and the Jebel Musa on the African side. In 1661 the Spanish issued a Coin with an illustration of the Pillars and a scroll running across them, and many people suggested that a stylized version of this, with the scroll taking on the S shape, became the dollar symbol. A later version of the Spanish coin with the pillars of Hercules and two globes showing Europe and the Americas, often called the Globe Dollar, is shown at right . In the absence of an American coinage, this coing became the most common coin in use in many parts of the colonial Americas. When the Americas did decide to mint there own, they chose to copy the well known Spanish Dollar. IN a 1777 letter to Jefferson, the previously mentioned Robert Morris, writing as the Superintendent of Finance for the Continental Congress ilustrates how common the coin was when he wrote, "The various coins which have circulated in America have undergone different changes in their value, so that there is hardly any which can be considered as a general standard, unless it be Spanish dollars. These pass in Georgia at five shillings, in North Carolina and New York at eight shillings, in Virginia and the four Eastern States at six shillings, and in all the other States except South Carolina at seven shillings and sixpence, and in South Carolina at thirty-two shillings and sixpence." Although the Pillar dollar was common, there is again no evidence that it was ever copied as a symbol.
Pesos and Pieces of Eight The Spanish Dollar that was so common in the Americas had a value of 8 "reals" another unit of Spanish Currency, and so they were called "pieces of eight" just as in the pirate stories. Another theory of the creation of the Dollar was from the abbreviation of "Pieces of 8" into an overlaid p8. As the p begins to look like a single stroke, and one side of the 8 gets straight, the theory starts to make some sense. Alas there seems to be little support for it in documentation, but a similar theory, that the $ dervied from a shorthand for the word "peso" seems to bear more fruit. Cajori shows a series of different notations between 1600-1800 from Spanish notes and ledgers that support the emergence of the $ symbol from this origin. The symbol for peso was sometimes written ps and as people made the p with just a single stroke, which it appears was not uncommon, and then continued the s in a single stroke, produced a number of symbols very like the $. The dollar mark may have just been sitting in the wings waiting to leap out because in 1776, Ezra l'Hommedieu, a member of the New York Provencial Assembly had over a dozen different symbols in his diary beginning with a single vertical bar and proceeding to two vertical bars. Only two years later a letter from Oliver Pollock to George Roger Clark shows the same amount using the $ in one case and the ps in another. A strong documentary support for the "peso" origin. Additional support may be given by the fact that the Spanish write the peso symbol after the amount, while the English colonists wrote the symbol for pounds in the front. The occasional apperance of documents by English writers with the $ after the number seems to suggest its Spanish origin as well
The Dollar seems to have emerged as a symbor very quickly after that. Cajori sights a document from 1778 with thirty-four subscribers to a theater, including George Washington. The signers indicated the amounts with "Dollars", "Doll.", or "D.". Not one used anything like a $. But by 1797, the symbol appeared in print, in a slightly altered version, in an arithmetic text. In American Accomptant, author Chauncey Lee suggested four symbols for the Federal money created by the Act of Congress of 1786. For the mill (1/1000 of a dollar) he used a single slash, /. For the cent, which was ten mills, he used a double slash, //. For a dime he used a single S across the two vertical slashes, which would be much like the present dollar symbol. For a dollar, the fourth unit of money, he employed four strokes, the two slashes, and two curved s like shapes across them. For the Eagle (Ten dollars) he used the E. Here is a copy of the Dollar symbol proposed by Lee from his book. Within a few years the symbols were found in print as the most common symbol for the dollar, Sometimes with two vertical bars, sometimes with one. Chaucey Lee's "double s" seems not to have caught on. I stil see many early documents with dollars and cents without a decimal point to seperate them, and Cajori gives a citation of a 1810 newspaper where the amount "One dollar and twelve cents" is written $1 12 with the 12 set apart rather than seperated with a decimal. I have not yet isolated the date when the decimal point with money began to appear, although the book by Lee mentioned above uses multiple decimal points in a single writing. Lee was a big proponent of decimal fractions and stated that, "vulgar (common) fractions are a very unimportant, if not useless part of Arithmetic."