What is the symobol of hades?

The Greek god of the underworld Hades has many symbols, however the one most associated with Hades is his Helm of Darkness. This powerful helmet enables Hades to,not just become invisible, but to become a part of darkness itself. It was forged in the first battle of gods v.s titans by the cyclops. It is said that,as all rational creatures fear the dark the wearer could make you go insane or stop your heart.