I would say install them so the end of the slot that has the slowest surface speed, enters the pad first, when moving in the foward direction.
Ken; I have the CenterLine type solid wheels, and can't see the rotors. Real shame, as they look great. Frank's look really nice. Now if he would get rear discs.........
I can tell you that MOST European cars have the slots facing the way that Earl has them(BMW M3's and M5's, to be exact). This "throws" the brake dust and gases outward away from the rotor . . . . However, S class Mercedes use the same rotor for the left OR right side . . .these are factory slotted rotors Before you start yelling at me for comparing a Mercedes to a Mav', just realize that friction is friction! I think Earl has it correctly. Now put an "M" on your decklid and start hanging out at Starbucks and nobody will know the difference!