Unfortunately, the Flag Code does not offer much in terms of clear and concise guidance. There are two schools of thought with regards to the display of a flag decal on an automobile.
First, when a person is walking forward with a staffed flag “aloft and free” the blue union would be forward. So one can argue that the blue field of the flag decal would face forward when placed on the side of the automobile. This is the preferred method.
However, the same methodology from reading Flag Code section 7(i) with regards to the display of the flag from a wall can also be applied, namely that the blue union would be in the upper left hand corner (observer’s).
Either display technically would be correct.