Sig Mak Gan is not one item but an effect that occurs when three artifacts are brought together. The three artifacts are the Scion Stump of Lukoon, the Shield of Thular-Tûr, and the Matter Penetrator.
When Naraz-Nâru was but an angel serving under the Covenant war-master Bal-Kriav, he made three artifacts to destroy the Entropy Arch at Piranoth Cyst. These items were made in a mighty cauldron inside the belly of the primordial Dališar. Naraz-Nâru forged a gauntlet, a shield, and a pick-axe. When used together they were called Sig Mak Gan - in old dwarven script, "three forces stability". After Naraz-Nâru destroyed the Entropy Arch at Piranoth Cyst, he gave each of his items to a separate Archangel.
... our victorious angels looked for a means to shatter the arch and seal this gateway to Chaos. Great magic, divine spells, and physical attacks failed to affect it. So, I forged three relics. When combined, they should be able to destroy the primordial device. The Sig Mak Gan is our only hope in destroying this Entropy Arch.
... with shield, gauntlet and pick-axe, I laid a dozen blows against it. It fell under Sig Mak Gan, purging the world that Bal-Kriav so nobly died for.
... to safeguard these great items, each will be put in the security of an Archangel.
- Naraz-Nâru, from an ancient scroll - "Arch of Chaos"
Over thousands of years, these items were changed in some ways to hide them from anyone seeking them out. An angel named Lukoon was given responsibility for the gauntlet. Later when he became a god, Lukoon figured the best place to hide the item was in the body of one of his sons. When Lukoon lopped off his son's hand, the item thereafter became known as the Scion Stump of Lukoon.
The shield was given to an angel named Atlas. In the Conclave War, a shield was looted and became property of a Khazarkar from the Urkuzîr family. It has remained in the possession of the Urkuzîrs for almost a thousand years. During one of the times this shield was being re-magicked, the god Atlas replaced the old shield with an exact replica. The replica is the shield forged by Naraz-Nâru. Though it is now an artifact, it is still called the Shield of Thular-Tûr.
The pick-axe was the ward of Arcana. This item, the most powerful of the group, was kept hidden for thousands of years. During the Volgad's problems with the fire giants of Borngring, she gave the weapon to a legate of the Šukhan Legion. The legate's name was Amrî Khêru. He and a group of other Šukhan wizards used the pick-axe to carve a piece out of the Cube of Arcane. Their intent was to use this piece of the Cube to halt the advance of lava rivers flowing into Volgad territory. Khêru named the item "Umân Yônul", which translates into the words Matter Penetrator.
The powers of the three items when combined have not been witnessed since the Dawn Era - so the powers of Sig Mak Gan are unknown.