I live in a snowy state. Never heard of any such law, never heard of anyone getting a ticket for anything related. The state could make a bundle if they enforced a law like this b/c EVERYONE would be pulled over and ticketed!!
In fact...........I've NEVER heard of anyone having ANY damage to their vehicle from snow/ice falling off of another moving vehicle. Ever. Nobody. Ever. Not a single person of my acquaintance. I'm sure someone here will be from Texas and know of a person who knew a person that had a cousin that had to replace a windshield from snow falling off of another vehicle.
I could give you an alphabetized list of those I know that have totaled their vehicles from hitting deer running across the street. Now that's scary!