This sidequest is MISSABLE, as once you beat the main story missions, you will not be able to do this, so make sure you don't skip this one. When you have completed Alien Abduction, the green goo will start spreading throughout South Park and Nazi Zombies will start appearing. Once this happens, head to the police station and talk to Sergeant Yates on the right.
He wants you to kill the zombies and bring back 5 Nazi Rings. Basically, just go around searching for the zombies and kill them, looting the rings off their bodies afterwards until you have five. Bring them back to Yates and he will become your friend on Facebook.
