"No person shall drive any motor vehicle with any sign, poster, sticker, or other non-transparent material upon the front windshield, wings, deflectors, side shields, corner lights adjoining the windshield, or front side windows other than a certificate or other article required to be so displayed by statute or regulations."
https://drivinglaws.aaa.com/tag/windshield-stickers/
It's from AAA so I imagine it's a somewhat credible source.