Yin yang amulet

The Yin yang amulet is only for show and offers no stat bonuses. Players can purchase this item from the Make-over Mage located south-west of Falador and north of the Crafting Guild for 100 coins.

The Yin yang amulet was made untradeable after some players sold the amulet for a substantial amount higher than its actual price. Some players believe this restriction should now be lifted, as the subsequent additions of the Grand Exchange, Trading limits between players and the trading interference showing the worth of items makes the scam unlikely now.

The Amulet's history
According to the Make-over mage's (Pete/Peta) comment on the Postbag from the Hedge, he found the amulet (non-replica version) from a drop of an extinct Gazulibird. As he picked it up and wore it, Pete's hair grew to his waist, and his gender was changed.

Trivia
Yin and Yang is the Chinese philosophy that influences everything and must be kept in balance.