Where does the dollar symbol "$" come from?

The original dollar symbol $ had two lines through it not one. I read about 7 different origins. Does anyone know the correct origin. like one i read the $ with two lines not one is suppose to spell ISIS after the Egyptian Goddes ISIS. also on the back of the dollar there are other egyptian symbols, pyramids and so on, so that ISIS is a possiblity.

The United States Abbreviation Theory
One of the most popular theories is that the dollar sign is derived from the initials of the United States. If you superimpose a capital "U" on a capital "S" then drop the lower part of the "U", what you end up with is a version of the dollar symbol with two strokes. This theory was endorsed by the American libertarian philosopher and staunch defender of capitalism, Ayn Rand, in her novel Atlas Shrugged. Chapter 10 is entitled the Sign of the Dollar. Rand claimed the dollar sign was the symbol not only of the currency, but also the nation, a free economy, and a free mind.

The Peso Abbreviation and Piece of Eight Theories
However, a more widely accepted theory nowadays is that the sign owes its origins to the Spanish peso.
One version of this theory is that the standard abbreviation of "peso" was simply "P", but the plural form was a large "P" with a small "s" above it and to its right. This was simplified by retaining only the upward stroke of the "P" and superimposing the "S" upon it. Hence the symbol of the dollar.

If the peso abbreviation theory is the correct one why is the US dollar sign sometimes written with two vertical strokes? A possible explanation is that the best known Spanish Peso coin had two pillars engraved on the reverse side to symbolize the "Pillars of Hercules" at Gibraltar and the words "Plus Ultra" indicating that beyond the Pillars of Hercules there were other lands. That coin was called the Pillar Dollar in the British colonies in North America and the two pillars may have become the two strokes in the Dollar sign.

There is another version of the theory linking the sign to the Spanish peso. As mentioned earlier the peso was subdivided into eight reals, hence the name piece of eight. This was represented as P8 or /8/. Eventually it became customary to write the oblique strokes across the figure 8. In the past precious metal coins were sometimes split into pieces to provide small change. The use in America of the expression two bits for 25 cents is a legacy of this since if a Spanish dollar or peso or piece of eight was split into quarters each part would consist of two of the original eight pieces or reals.

The 8 with two strokes became a letter S with two strokes since S looks like an 8 that has been split, as when a peso was broken to provide change in reals. Eventually a further simplification was introduced by dropping one of the strokes.

More theories below.
Source(s):
http://www.pballew.net/dollar.html
http://projects.exeter.ac.uk/RDavies/ari…


- On en.wikipedia.org -

Originally the peso sign, $ (called dollar sign in English) is a symbol primarily used to indicate the various dollar and peso units of currency around the world.

Origin

The sign is attested in business correspondence between the British, Americans, Canadians, and Mexicans in the 1770s, as referring to the Spanish-Mexican peso, known as "Spanish dollar" or "pieces of eight" in British North America where it was adopted as U.S. currency in 1785, together with the term "dollar" and the $ sign.

The origin of the "$" sign has been variously accounted for. The most widely accepted theory is that it derives from the Spanish coat of arms engraved on the Spanish colonial silver coins, the "Real de a ocho" or Spanish dollars that were in circulation in the Spanish colonies in America and Asia. The Spanish dollars were also legal tender in the English colonies in North America, which later became part of the U.S. and Canada.

In 1492, King Ferdinand II of Aragon adopted the symbol of the Pillars of Hercules and added the Latin phrase Non Plus Ultra meaning "no further", indicating "this is the end of the (known) world." But when Christopher Columbus discovered America, the legend was changed to "Plus Ultra", "beyond."
Spain's coat of arms

The symbol was adopted by Charles V and was part of his coat of arms representing Spain's American possessions. The symbol was later stamped on coins minted in gold and silver. These coins that depicted the Pillars of Hercules over two hemispheres and a small "S"-shaped ribbon around each, were spread throughout America, Europe and Asia. For the sake of simplicity, traders wrote signs that, instead of saying dollar or peso, had this symbol made by hand, and this in turn evolved into a simple S with two vertical bars.

There's another documented explanation that states that the sign is the result of the evolution of the Spanish and Mexican scribal abbreviation "ps" for pesos. This theory, derived from a study of late eighteenth- and early nineteenth-century manuscripts, explains that the s gradually came to be written over the p developing a close equivalent to the "$" mark."