Ideas for Texture?

I am completly new to picture editing and I dont think I am very talented when it comes to stuff like that, but I started playing around with the texture of Carper(ino)s new Charger. I came up with the idea to make a Traffic Unit skin for it because it maches very well with the lights and I asked in the forum if anyone knows if there is already something out like that and noone replied.

So I started with some really basic stuff and its definitly not the greatest, but I personally like it...So my question now is, does anybody have a tipp what I can do turn this into a "Traffic Unit" while keeping the original skin design? I couldnt find much about in the internet and due to the fact that I am german I cant use real life experience :D

Unfortunatly, there is alsonot much space on the back of the car for additional marking etc. So pls tell me your thoughts about that and what u think i can do, what I can improve or if u have other important tipps when it comes to textures!