Are they orange slices ... bicycle wheels ... or some poor guy's cracked eyeglasses? :-)
I never did ask what the logo of the city of Mainz actually stood for! Anybody else have better ideas?

Update: According to http://en.wikipedia.org/wiki/Wheel_of_Mainz , the coat of arms "... is derived from the coat of arms of
the Archbishops of Mainz and features two six-spoked silver wheels connected by a silver cross on a red background".