amulet

An amulet (from Latin amuletum; earliest extant use in Natural History [Pliny], meaning "an object that protects a person from trouble"), a close cousin of the talisman (from Arabic طلاسم tilasm, ultimately from Greek telesma or from the Greek word "telein" which means "to initiate into the mysteries") consists of any object intended to bring good luck and/or protection to its owner. Potential amulets include: gems or simple stones, statues, coins, drawings, pendants, rings, plants,animals, etc.; even words said in certain occasions—for example: vade retro satana—(Latin, "go back, Satan"), to repel evilor bad luck.

http://en.wikipedia.org/wiki/Luck

http://en.wikipedia.org/wiki/Charm_bracelet

The wearing of charms may have begun as a form of amulet to ward off evil spirits or bad luck.

In ancient Egypt charms were used for identification and as symbols of faith and luck. Charms also served to identify an individual to the gods in the afterlife. Medieval knights wore charms for protection in battle. Charms also were worn in the Dark Ages to represent family origin, religious and political convictions.