Ever hear of Kentucky Wonders??? That is the long full width rear mud flap often seen 50's - 70's .
I wouldn't call these "adorning" anything. They were rarely installed for looks. These were marketed as a practical accessory for staion wagons. These flaps stopped the spray from forming under the car (to a large extent), which then did not fly up behind the car and adhere to the back window blocking the view. They were later supplanted by the airfoils applied to the side and top of the tailgate. The rear wiper (now ubiquitous) was a better solution.
If you ever saw one on a sedan, however, it was strictly for looks! <img src="http://forums.aaca.org/images/graemlins/crazy.gif"