Did you know? The sign "$" actually means "peso".
http://observationdeck.io9.com/why-is-the-dollar-sign-a-letter-s-16839405751. Where does the word "Dollar" come from?
The "Joachimsthaler" was an important standardized coin in the early 16th century. (Joachimsthal means "Joachim's valley", which lies in Czechia in the former kingdom of Bohemia.)
The word "Thaler" for coins spread to many other languages. In the english world it became "dollar".
2. Where does the sign $ come from?
Conquering Central America made the kingdom of Spain filthy rich. Mid-16th century they issued a new standardized coin that became the new standard for international trade, the "real de a ocho" ("real" being the name of the spanish currency). But more colloquially, the coin was called "peso de ocho", "piece of eight".
Now, where did the sign $ come from? Bookkeeping. The "peso" was the go-to currency for international trade after all.
By the 1770s, the abbreviation was complete and the symbol $ had reached its current form.
= new reply since forum marked as read
Updated version, accounting for inflation. 
A common theory holds that the sign derives from the Spanish coat of arms, which showed the Pillars of Hercules with a banner curling between them.
In 1492, Ferdinand II of Aragon adopted the symbol of the Pillars of Hercules and added the Latin warning Non plus ultra meaning "nothing further beyond", indicating "this is the end of the (known) world". But when Christopher Columbus came to America, the legend was changed to Plus ultra, meaning "further 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, depicting the Pillars over two hemispheres and a small "S"-shaped ribbon around each, were spread throughout America, Europe and Asia. According to this theory, 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.
http://en.wikipedia.org/wiki/Dollar_sign#Spanish_coat_of_arms
Specifically, the pillar on the right side. This coin circulated in the 13 colonies, where it was called a "Spanish milled dollar". The 2 reales ("2 bits"
coin became the US quarter.
and several of the smaller denominations from that period. I also have a few silver Spanish coins from the Revolutionary War period (with the portrait of the ugly guy with the big nose-- Carlos IIII), and a couple of gold 4 scudos from that time as well. As you said, it is amazing to think of the stories those coins could tell, especially considering that they may have circulated in the United States as legal tender up to 1857.
And you are right about the Mexico City mintmark-- an M with a circle above it, which is still used today. 
Thanks for getting my hopes up, then crushing them. I thought for a minute there I wouldn't need to go to work today
All sarcasm btw... thanks for the trivia fact, and I actually do need to get going to work. Have a good day!
