So I read somewhere that ford put these little clips on the rotors during assembly. The reason I looked into this I because I've had my new wheels balanced multiple times and still they were "out of balance". Come to find out its these stupid little clips causing it. If you have this issue pull off your wheel and look if you have these clips as well.
Yep, very common oversight for lots of people. They are only there to assist while the car is being assembled on the line, and non-Ford wheels do not have a machined recess in the back of the wheel to accommodate it.