Stellazzio Coins can be found all around the world and are wanted by a noble called the queen of Stella in Treno. (EDIT: So they are actually called Stellazzio Coins, not Stellazzios, so that might've confused you.)



There are a total of 13 of them. Finding them and bringing them to Stella can get you some nice items (a Blood Sword, Black Belt, Rosetta's Ring, Robe Of Lords as well a grand total of aproximately 60,000 gil). The 13th reward, the Hammer, is also necessary to view FF9's secret extended ending. You only have to have the Hammer in your inventory to see it when you finish the game.

The locations of the coins can be found here:
http://www.square-central.com/ff9/coins.shtml