Funny, I have never before seen or heard of the "pawnbroker's symbol". I looked it up and I guess you mean the three circles hanging from a line. Is it a regional thing, I wonder? Here in the western USA, the only sign I would associate with a pawnbroker is "dingy neon". I wonder if the traditional sign is still used in areas which had pawnbrokers before the invention of lighted signage.

Certainly British, and probably European, usage. And yes, it predated electricity by quite some time, in fact said (http://en.wikipedia.org/wiki/Pawnbroker) to date back to the origins of banking in Italy.