I think that a magic ring, in addition to, the bond would be excellent. It fits in with the 'Mage' archetype. It's also not too busy so as not to distract from the already cool trench coats. While maybe not noticeable to others it would be the most noticeable to the player him/herself in first person. The rings, being circular, could just be copies of the bonds. Removing the need for extensive redesign.