PRoblem is, the law REQUIRES that they be marked - an oft-ignored law, I admit, but unless a vehicle is being used specifically for investigation it must be at least minimally marked. Wouldn't have to have the full decal job, but it is legally required to be marked, ALL PUBLICLY OWNED vehicles are. (And it has nothing to do with the plate, so long as it is publicly owned, it is covered - that is state law.)