Mercedes-Benz CL Operator's Manual page 420

Features
418
Vehicles with Night View Assist
Areas permeable to radio waves (to the
:
left of the rain sensor cover)
Rain sensor cover
;
Areas permeable to radio waves
=
In order to operate radio-controlled
equipment, e.g. toll recording systems,
areas : and = on the windshield are
permeable to radio waves. In these areas, you
can install radio-controlled systems.
These areas can best be seen from outside
the vehicle by observing the light reflected off
the windshield.