This week I ran across a site that keeps looping me into further links. At some point, this popped up: http://www.todayifoundout.com/…e-dollar-sign-comes-from/
Spanish peso coins were designated (plural) as a 'p' followed by a superscript 's,' which eventually became entertwined, then abbreviated to an 's' with a single or double vertical slash taking the place of the 'p.' Because Spanish coins were commonly used in North America, with a 1:1 value with the dollar, the symbol that now is used as a dollar sign was adopted.
(The original site that led me down the time-devouring path is called simply "Today I Found Out: Feed Your Brain."
http://www.todayifoundout.com. I defy you to go there without losing an hour or more --)