It is a cover.
The Picture dont help.
Does it ever light up at night? I know the town car has some ambient lighting at night and it could be part of that system.
The parchment is the headliner.....so the sensor parchment is the piece of the headliner that holds this "sensor".....that the government is listening in on your ganster rap through. haha
You have automatic A/C with passenger and driver settings separate right?