Anger is a great business, people will share it with you for free and if you're savvy enough, you can sell it back to them. The Rage Mages descended from Belligerus's early followers have found that modern world has just as much use for anger and magic as the ancient world.
The idea of using tattoos to contain magic powers is not a new one. The Ink gauntlet follows the basic premise of using rare and precious inks to inscribe spells into the skin of a mage or would be spell-imbued person. Some of these inked spells might be permanent, while others might fade after being used once, or a preset number of times.