As far as I can see Mercedes already devalued the AMG badge when they put it on all the carpet mats and wheels. What difference does it make sticking it on the back as well? Personally I have no badges on my cars at all. But everyone looks at the wheels, floor mats and steering wheels, puts 2 plus 2 together and makes 5. I just smile and say, "it's diesel though...."Don't do it! That is the one AMG retrofit that I would never do to a non-V8 AMG.
You're driving an SLK so you can't be totally tasteless....I guess I have no taste or breeding lol