Phra means Monk or amulet and Pidta means close eyed. It is an ancient symbol of protection (derived from deep meditation states).
The wearing of this amulet is now considered proof against guns, but as this symbol predates fire arms by millennia, it may be considered general protection.
Terra cotta Phra Pitda statue sits in a clear jewel-box case surrounded by 18k gold. A popular devotional item in Thailand, where we buy directly from the jeweler/artisans who create them.