Hades is neither evil nor good. He is the lord of the underworld. He is only evil in the sense that death and dying is evil. It is something that all creatures go through, so it would be like being...
Hades' symbols were (or are whatever you wanna say) his helm of darkness/invisibility. it could make him invisible. his other symbol is a two-pronged staff (like Poseidon's trident without the middle...