Huge Blind Spot on Board

Yesterday while driving through Highland Park I saw a pickup truck with a sign that took up the entire back window that said something about seat belt safety. Did it occur to the driver that their entire rear windshield is covered, thus rendering another rather important safety device, the rearview mirror, completely useless?



I'm sure the sign bearer's intentions were all good ones, but maybe they should change it to display this important safety message:

CAUTION: I MAY ACCIDENTALLY CUT YOU OFF

BECAUSE I CAN'T SEE YOU THROUGH

THIS BIG FUCKING SIGN IN MY WINDOW