Brake pad residue

Is it normal to have excess brake pad residue on the outside of open faced wheels. A friends car has a lot of what I think is brake pad residue on the outside of the open wheels where you can see some of the brake pads. The pads look good but I have not taken off wheel to check. I was wondering if it could be something else or if it was the pads. The residue is a thinck dust that smears like it has oil in it but doesn't seem like it. It is smeared all over both front wheels on her newly purchased car but the car is a couple of years old. It is not on the back wheels at all, only the front. It is a ford escape about a 2003.