Why do Mercedes W124's put a fog line on the windshield? I have to use my windshield wipers on hot dry nights in the summer.

Also, my fan is squealing. I did some searching on this forum, and found there's some fan kind of thing that needs to be oiled, behind the glove compartment. Can anyone second that? Seems very easy to do. But when the blower fan is off, there's no noise. So does that mean it's the blower fan, or the thing behind the glove box?