"This sign is said to have been used on the Coat of Arms of the Medici family and thus comes from Italy of the Middle Ages. The Mediciswere extremely rich and great lenders of money. For this reason and have become symbols for pawnshops, and pawnbrokers."
From the "Online Encyclopedia of Western Signs and Ideograms" at SYMBOLS.COM
The pawnbroker's symbol is three spheres suspended from a bar. The three sphere symbol is attributed to the Medici Family of Florence, Italy, owing to its symbolic meaning of Lombard. This refers to the Italian province of Lombardy, where pawn shop banking originated under the name of Lombard banking. The three golden spheres were originally the symbol which medieval Lombard merchants hung in front of their houses, and not the arms of the Medici family. It has been conjectured that the golden spheres were originally three flat yellow effigies of byzants, or gold coins, laid heraldically upon a sable field, but that they were converted into spheres to better attract attention.
Most European towns called the pawn shop the "Lombard". The House of Lombard was a banking family in medieval London, England. According to legend, a Medici employed by Charles the Great slew a giant using three bags of rocks. The three ball symbol became the family crest. Since the Medicis were so successful in the financial, banking, and moneylending industries, other families also adopted the symbol.
Saint Nicholas is the patron saint of pawnbrokers, and the three suspended spheres symbol has also been attributed to the story of Nicholas and the three bags of gold. Throughout the Middle Ages, coats of arms bore three balls, orbs, plates, discs, coins and more as symbols of monetary success.
Pawnbroking can be traced back at least 3,000 years to ancient China. In Hong Kong it follows the Chinese tradition, and the counter of the shop is typically higher than the average person for security. A customer can only hold up his hand to offer belongings and there is a wooden screen between the door and the counter for customers' privacy. The symbol of a pawn shop in Hong Kong is a bat (the animal) holding a coin, the bat signifies fortune and the coin signifies benefits.
In the west, pawnbroking existed in the ancient Greek and Roman Empires. Most contemporary Western law on the subject is derived from the Roman jurisprudence. As the empire spread its culture, pawnbroking went with it. Likewise, in the East, the business model existed in China 3000 years ago no different than today, through the ages strictly regulated by Imperial or other authorities.
In spite of early Roman Catholic Church prohibitions against charging interest on loans, there is some evidence that the Franciscans were permitted to begin the practice as an aid to the poor. In England the pawnshop came in with William the Conqueror, with an Italian name, Lombard. In 1338 Edward III pawned his jewels to the Lombards to raise money for his war with France. King Henry V did much the same in 1415. The Lombards were not a popular class and Henry VII Tudor harried them a good deal. In the very first year of James I Stuart an Act against Brokers was passed and remained on the statute-book until Queen Victoria had been on the throne thirty-five years. It was aimed at the many counterfeit brokers in London.
The Medici family crest has long been the object of much historical speculation. The most romantic (and far-fetched) explanation of the origin of the palle is that the balls are actually dents in a shield, inflicted by the fearsome giant Mugello on one of Charlemagne's knights, Averardo (from whom, legend claims, the family were descended). The knight eventually vanquished the giant and, to mark his victory, Charlemagne permitted Averardo to use the image of the battered shield as his coat of arms.
Others say the balls had less exalted origins: that they were pawnbrokers' coins, or medicinal pills (or cupping glasses) that recalled the family's origins as doctors (medici) or apothecaries. Others say they are bezants, Byzantine coins, inspired by the arms of the Arte del Cambio (or the Guild of Moneychangers, the bankers' organization to which the Medici belonged).
(The following basic information is a summary taken from the free online encyclopedia at Wikipedia).
Note: For a facinating look at how they helped influence commerce today, here's a great site to visit for a glimpse into the Medici family history