It's red, it's unfortunately very tiny, and (yes) it is a thong worn for good luck by the 6'4", 234 pound Giants first baseman. And very often in the Giants clubhouse, that's all Huff is wearing.
Some teams have a lightning bolt, or a screaming eagle, or a sock as their official symbol. The Giants have a red thong.
Kudos to Ashkon Davaran for this way sick reminder of that very uncomfortable fact: