
Visible crew/equipment: When Barney and Floyd are spying on Sam while he's getting groceries, we can see both of the grocery store's windows and its clear glass, but when Sam drives off the left display window has been covered with a dulling spray resulting in a matte surface, to prevent the camera and crew's reflections.
Answer: Those "boxes" are valences that used to be very common, before air conditioning. They allow for windows to be open during rain storms. They permit air circulation, without letting the rain in.