As a unique champion who constantly moves, Signed was bound to take a special role. Currently right now though he can be used in a way that should not work, He will wander into champions attack range and then wander out again and the champions who targeted him previously will now chase him all over the map come hell or high water! That means you can have your mage aimlessly wandering around your backline or your melee carry running in circles while being shot instead of attacking.
I would suggest including a targeting repriority, that if a champion leaves your attack radius (which previously didn't happen that often) the champion looks for the new nearest target putting Signed at the lowest priority (so onyl chasing him if noone else is in equal range). That should prevent signed from randomly just making your team 'do nothing' while they play tag with him.