The NHTSA might interpret the 'tubercules' as a pedestrian safety hazard,for when the mirrors are folded and folks in parking lots are passing by,to and from shopping.
Since the serrations don't provide any boat-tailing,they may not affect the base pressure of the mirrors wake,but since there is a zig-zag differential separation line,there ought to be some significant vorticity and shearing which might break down larger eddies,kinda homogenizing the wake.This is a concept BicycleBob spoke about years ago.
These smaller eddies might succumb to quicker viscous attrition,killing the mirrors wake in less distance/time,while reducing its effect on interference drag.
