Hermes' Coin was one of Ten Godly Possessions found in God of War III.
Using it during Bonus Play disabled new Trophies from being unlocked.
Collected 10 times the amount of Red Orbs.
Its effect was similar to the The King's Ring from Ghost of Sparta.
Either before or after killing Hermes, in the room with the severed head from the Statue of Athena, collect Hermes' Coin near her left ear, which was out of view of the camera.