I remember when the fight occurred on the "Live Free or Die" stamped onto New Hampshire license plates. That also was court-challenged as a "religious statement" by a couple of historically "Conscientious Objector" groups. They lost.

In this day and age, the states have just gotten into the bumper-sticker business via license plates as a revenue enhancement scheme. Whether it's a sports team, college, military service, radio call sign or cause, it can be gotten on a license tag as long as it is not "profane" and enough people are willing to pay the costs (determined by marketing, not philosophy). It's not mandatory, and comes with a higher fee (to cover tooling, manufacture, distribution and profit).

Considering what I've seen stuck on car bumpers and trunks, it is subtle and definitely a matter of personal choice. Call it what it is - automotive jewelry!