What is the sensor on rear right (facing forward) of the RR mirror?

Does anybody know what the sensor (or whatever it is) is that’s on the right rear (facing forward) of the rear view mirror?
I can’t find it in the owner’s manual and it’s not listed as part of the Honda Sense. I don’t think it’s the auto-dim for the mirror since that has 2 sensors facing rearward. And I don’t think it’s the auto-on for the headlights since that’s the bump in middle of dash near to the windshield (verified by covering it up and auto-on stopped working). I’m stumped.

My WAG would be maybe it’s a photocell to keep mirror auto-dim from activating in daytime? Anybody know for sure?

 

Thanks megrayhair! I needed to know that to make sure it was ok for my handicapped tag to obscure the view of the road to it as long as it doesn’t block light getting to it.