United States Flag Etiquette

United States Flag Etiquette dictates that flags be reversed on the passenger side of moving objects, such as vehicles.

"The blue field of stars should always be in the highest position of honor [...] When displayed on a "moving object" like a person or vehicle, the highest position of honor is the front, and not the rear; so the field of blue should be displayed to the front."

You can read more about flag etiquette here:
http://www.marlowwhite.com/faq/f-why-is-the-flag-patch-reversed.html