As title, i noticed the other day when washing the car, on the inside and outside theres a 3" by 3" section of window that feels like sandpaper, not sure what it is but it does move/come off slightly using my finger nail but i cant get it all off properly that way, and ive tried squirting window cleaner onto it and rubbing etc but it just wont shift?

I was thinking clay might work as ive heard it can be used on windows? do you think that would get it off? or any other product i might already have and not thought of?

Cheers