It is simply an indicator to tell the user how to make the Orb reveal the location of the Cradle of Life. On the front is the image of a person blowing through a horn. It shows that sound is the key to the Orb, but only a certain set of sounds work.
The novel of 'The Cradle of Life' says that the Medallion is found in the eye of the statue of Alexander in the Luna Temple. It also says that it is made of copper and had turned dark with age. There is an image on one side of a seated figure playing a musical instrument.
In Greek mythology, Zeus ordered Hephaestus to create a human woman called Pandora as a wife for Epimetheus - Prometheus' brother. This was revenge against Prometheus for stealing fire and giving it to man. She was made to be full of love and persuasion. Zeus gave Pandora a box and warned her not to open it. Inside it contained all known evils such as greed, jealousy, slander and vanity. Pandora, being human, was naturally curious and couldn't resist opening the box. Learning of what was inside, she tried to close it before the evil forces escaped but she failed. They flew out into the world, plaguing mankind. It is said that hope was the last thing to come out of the box before Pandora cried black acid from her eyes, knowing that she had done a wrong thing.
The Orb contains the location of the Box.