That extra antena is for the Satelite radio, but on production cars it will look like this:



a little bubble, not another antenna like the one on the roof.

I guess MBUSA wanted to go with "550" to emphasis the change over the old S500 and keep the naming system truthful.

I wonder if the E/CLS/CLK/R/ML will all change from 500 too 550 for the U.S. market when they get the new V8? Likely.

M