it’s an ancient symbol - a snake, around the tree of life.
Cite (or picture) please? 
I can’t site my source and I may well be wrong but I remember when I asked this many, many years ago, the answer I received seemed quite feasible: The the $ used to be U and S overlying each other and that the bottom of the U was simply cut off later. While this may not answer definitively, it’s sure seems practical, doesn’t it?
Um, Cliffhanger, you might want to read the original article? It’s here: What does the S in the dollar sign represent? - The Straight Dope
Cecil mentions the overlapping U and S theory as one of the urban legends that sounds great but has no basis in fact.
From Cecil’s original column What does the S in the dollar sign represent?:
The subject of the dollar sign was close to Professor Cajori’s heart, and he could get quite indignant on the subject. As he tartly noted in his book, “About a dozen different theories [on the dollar sign’s origin] have been advanced by men of imaginative minds, but not one of these would-be historians permitted himself to be hampered by the underlying facts.” Among the deficient hypotheses:
(1) The dollar sign was originally the letters U and S superimposed. The idea here is that the original dollar sign had two vertical lines, not one. Popular though this idea is, there is zero documentary evidence for it. Furthermore, Robert Morris, the Revolutionary War financier and the first U.S. official to use the dollar sign, made it with a single vertical stroke.
lol I had read it. I meant where I’d heard it from was much, much earlier and that it seemed the most feasible and practical. I understand there’s no evidence to support it but I also believe it’s possible that this is being made harder than it has to be. That’s all. By my saying “made harder than it has to be”, I mean its origins, not the theories people are bringing forth. Admittedly, I had forgotten about the Robert Morris part though. OOPS! Carry on…
BTW, could it be that behind so many theories is that people simply can’t wrap their heads around the idea that once upon a time the peso was the standard for “hard currency” in this part of the world?
There’s strong evidence against it, in that it was being used before the US existed.
Not just in “this part of the world”. Due to Mexican and Peruvian silver, the Spanish Dollar [or “piece of eight” of pirate-themed legend] was a sort of universal proto-world currency …
I’m thinking they may be misremembering the theory that it’s based on the Caduceus (a common symbol for commerce, before it was confused with the Rod of Asclepius and thus misapplied to medicine) - though the Caduceus and RoA are both staves twined with snakes, not trees.
(Also, the theory has a major flaw in that the Caduceus has two snakes, not one, so a resultant symbol would look more like a crossed 8 than a crossed S.)
THAT’S very interesting! I was in fact, thinking of the Caduceus when I asked for a cite. I did not know that there was another, that looked similar. :smack:
Ignorance successfully fought, once again! 
Thanks, Tengu! 
Here’s a pretty good link explaining the difference between the two symbols that Tengu referred to.
I have to say the story that seems most plausible to me is that it comes from the Pillars of Hercules design on the Spanish *real *coins. The pillar on the left certainly looks very much like the dollar sign we know today.
(OK, this particular coin is from 1799 and so post-dates the origin of the $ sign, but it’s an iteration of earlier similar designs which were around from at least the 1730s.
Nothing to do with sal (salt), either, which Romans used to pay their soldiers (thus the word salary). Just thought I’d mention.
It was obviously chosen because it’s the only symbol on ASCII that is exactly the same when turned upside down. [/silly mode]
0h.
More to the point, the Columnario was specifically minted in and for the new world. The only real difficulty is that the evolution from PS to $ can actually be traced in old mss., and this theory can’t.
Ø rly? [/xtra silly]
What about % and ~ and #, aren’t those ASCII symbols? [/nit pick mode]
And I and H and O and 0 …
salutes, swirls cape, leaps out window