Is English your second language?
Putting up a flag is an activity; taking down a flag is an activity; having a flag on your vehicle is not an activity.
On the other hand, that PC management team would have their heads explode if he drove in flying the "Gay Pride" flag. Or the raised fist of "Black Power"...
Just Saying...
Perhaps you need to return to your ESL classes. Parking your car on someone else's private property is an activity. Whoever owns that property can set just about any rules they like regarding the conduct of individuals on said property.