The symbol we use today for the dollar, $, originally had two vertical strokes. In the 1877 book “Gold and Debt” by William Lyman Fawcett, the history of the dollar symbol is told.
The $ symbol was derived from the pillars of Hercules, one of the oldest symbols known to the human race. Their composition is due entirely to the emperor Charles the Fifth of Germany who, also being king of Spain, adopted them as supporters on either side of his escutcheon, and also placed them in the device on the Spanish “pillar dollar.” Charles derived the idea from the poetic conceit which gave the name of “Pillars of Hercules” to the two mountains which stand on either side the Straits of Gibraltar; that is, Calpe, or the Rock of Gibraltar, on the north, and Mount Abyla, in Africa, on the south. The scroll, which in the device on the dollar was twined about the pillars, has by long use been gradually modified through writing the mark so as to assume its present form in the dollar mark.