I would just use the first one joey made, only with a period instead of the roundel.
I think white would be the best choice for coloring because it would contrast perfectly with black tint. And would still be pretty visible on a non tinted car.. any other color would be harder to see and might clash with peoples car colors.
It would be nice if two colors were available.. white and black, so that people with un-tinted cars (like me
) could get a decal that stands out better.