The skeptron was a powerful weapon used by an alternate version of Shadowhunters in Edom against the realm's demons, the asmodei. Despite its power, the weapon only served to protect the Nephilim for a while before they were eventually overpowered and defeated.
It is an iron rod having a circular metal ornament at its tip in which a red jewel is embedded.
In 2007, Jace Herondale was able to retrieve a functioning skeptron, taken from a rigged statue of Jonathan Shadowhunter from the realm's Accords Hall. He used it against the demons sent by Sebastian Morgenstern.