OT: U-shaped slot in forehead region of helmets?

I haven't seen this discussed yet, and a quick Google search turned up nothing, but I noticed after watching a bit of the ND and MSU games that some of the players seem to have a U-shaped something right in the forehead region of the helmets. It looks like a cut through the plastic, but I can't be sure. I'm assuming this is some kind of head injury prevention thing, but does anyone have information on it? Has this been used before? Do any of the Michgan players have it?

I probably missed information on this somewhere along the way, so delete if needed.