Long before the cultivation of Buddhism and the dawn of Siddhartha's ascension to enlightenment, ancient Indian people wore jewelry painted or etched with sacred and religious symbols that represented their collective beliefs about life and the various phenomena of the universe. Many of these symbols are found in Buddhism today, and to this day, represent the same same things as they did then.
Take for instance, the swastika symbol. An although seemingly Buddhist symbol, it's roots actually date back to a time long before Siddhartha ever walked the face of the earth or enlightenment was a wide-spread phenomenon or achievement of life.
Many of the symbols found in Buddhism today, actually pre-date the formation of Buddhism. And contrary to popular belief, Siddhartha wasn't the first known man to become enlightened. There were many others before him who reached this milestone in life and were seen as small-time spiritual leaders within their collective societies. The only difference between them and Siddhartha, was that Siddhartha left us with a clear blue print or road map that we could follow to alleviate suffering and attain spiritual enlightenment.
However, over time as Siddhartha's teachings became more and more popular and widespread, these pre-existing ancient Indian symbols and their meanings were gradually branded into Buddhism and accepted as part of the faith. And so much of the origin of Buddhism and Buddhist jewelry didn't actually begin with Siddhartha. But extends back to a time in which much of Buddhism is founded on.