Make completing an event in each zone has a 0.1% chance to award you with a lvl 80 weapon that has an unique skin, these skins vary in each zone.
In some zones, you could also reward minis, back items, rings with unique stat combo, and so on.
Or make events award tokens (that can be deposited to a gethring tab), different in each zone, and tie a reward npc to them.
Captain Deutschland, Ozzy The Insane, Hanz Limbchewer – r40+ mes/nec/engi Desolation
Fear The Crazy [Huns]