Here you cant have anything that obstruct your view out the windscreen if you go by the law, but still people have a lot of "poo" on their windshields.
1: phones - tablets and / or NAV units, most often put right smack in the middle of everything. ( i have seen a car with one of each on the windscreen one on top of the other effercively making a wide illuminated bar down the middle of his windscreen )
2: stuff dangling from the mirror, mostly seen with people that have a heritage towards the deep south east, and most often of the muslin religion or use to be anyway.
But even pure bread Danes will do this too, pure bread Danes will even talk like a 1 generation immigrant, apparently as that's bad ass gangsta or something
But it matter little its not like it is something the police are bothered about, not even in COP programs on TV where they have a guy with a video camera running behind them.
They will happily fine you for speeding and or using a phone while driving, but the fat ass NAV unit right smack in the middle of the windscreen get no mention, or the beads and what not crab some people have dangling from the mirror.
According to the law even a thin wire are not allowed.
Personally i have a lot on my windscreen in the form of dashcams, but they are all above the mirror on the gritted area and only just peek below it, and i can barely see them behind the mirror from my driver position.
And i cam record all the video and audio i like, the problem arise in me posting some of it on youtube, but i will keep doing that until a judge tell me not to.
If you have a newer car with one of those large and silly sensor arrays down the middle of the windscreen, you might be able to mount off that, that's not the window as far as im concerned, but i figure its a matter of legal semantics.
Maybe have a look in the "where did you mount your camera" thread, start from the back / newest and work your way back in time and camera design.
https://dashcamtalk.com/forum/threads/where-did-you-mount-the-camera-post-your-pictures.502/page-54