These cars aren't looking through the windscreen. They're covered in sensors and probably use LIDAR system to navigate. They see in the dark and through fog.

It's fairly obvious where the sensors are located looking at the car. And because these cars are dumb as hell, it takes relatively little to disrupt their ability to tell the difference between say, a person the car has to stop for, and a cardboard cutout of Scott Bacula. Or a traffic cone, as another user mentioned though that particular exploit may have been patched out by now.

They stop and can't move again with a cone on the hood.

Do with that information what you will.

Someone is going to spray paint dicks on them