I call the clean Lexan thing on my road motorcycle helmet a shield. Same as they do for the eye protection for football players (American). I call the fashionable chunk of plastic over the top a visor. Same as it is on a baseball cap.
That said, if you remember that this all started with Shoei/Troy Lee’s very first MTB helmet that was more of a 3/4 coverage thing with a visor. It was this: https://factoryjackson.com/wp-content/uploads/2015/11/Shoei-RC3-2000x1333.jpg I think it was almost $200 US back in early 90’s bucks. That priced me out!
It was so “Moto” at the time and screamed style! It just looked so much better than the styrofoam-Lycra-panty covered helmets that you had to choose from at the time.
I got in to MTB from the motocross scene because all the MX guys (Bailey, O’Mara specifically) we’re riding MTB for training. I wanted to look like a MX guy, not a bike guy. Still wore Lycra shorts and tight jerseys with 3 pockets on the back because that was what there was, and dammit, that’s what we were supposed to wear!😆
Now get off my lawn!