The most likely is the theory that it comes from a handwritten ‘ps’, an abbreviation used in correspondence as a plural form of ‘Peso’. Manuscripts from the late 18th and early 19th century show the ‘s’ gradually being written over the ‘p’, and the upward stroke of the ‘p’gaining dominance over the curved upper part. This eventually developed into something resembling the ‘$’ sign. (see below)
- It is inspired by the mint mark on the Spanish ‘Pieces of Eight’ coin which became known as the Spanish Dollar. The coins were minted in Potosí in present day Bolivia. The mint mark was composed of the letters “PTSI” superimposed upon each other. The mark bears a strong resemblance to the single-stroke dollar sign (see photo right).
- The $ sign is derived from the Number 8, whereby the Spanish Dollar was originally a ‘Piece of Eight’. The P of Peso and the 8 were said to be combined. The modification would have occurred to avoid confusion between the number and the signal. – This explanation would however seem implausible, as the confusion between a number and currency sign would have probably been too great.
- The sign was inspired by the Spanish coat of arms engraved on the colonial silver coins which were in
circulation in Spain’s colonies in America and Asia. These coins, depicted the Pillars of Hercules a small “S”-shaped horizontal ribbon wrapped around each pillar. For the sake of simplicity, traders might have written signs that, instead of saying dollar or peso that may have evolved into a simple S with two vertical bars. – Highly speculative though plausible. (See picture on right)
- A dollar sign with two vertical lines could have started off as a monogram of ‘US’, used on money bags issued by the United States Mint. The letters U and S superimposed resemble the historical double-stroke dollar sign: the bottom of the ‘U’ disappears into the bottom curve of the ‘S’, leaving two vertical lines. Ayn Rand, the American libertarian philosopher, endorsed this theory in her novel Atlas Shrugged. However there is no documentary evidence for this theory though,.