Well, just my $.02, but if I saw that plate on that car, I'd think the owner was at best lacking in taste, at worst an adolescent j/o.
But, hey, I'm not the Fuhrer of Good Taste.

I have several m/c helmets pastered with stickers. The simple test I always used was would I be embarrased with one if my mother or daughters thought it was crude or embarrasing to them. Works for me.

Was it Justice Brennan or Stewart who said that he counld't define pornography, but he knew it when he saw it?
Good taste. Elusive concept.
Again, just my $.02.

In the interest of full disclosure, my plate on the 124C:
NJ: LYTINUP