You may wish to check this out
U.S. Scanner Laws among other "state scanner laws" Google will direct you to. That thing about a ham license is a bone of contention, how states handle it is problematical at best.
Amateur transceivers are exempt at the federal level but ONLY per their CAPABILITY to receive public service frequencies, USAGE is another matter altogether! In some states it is illegal to monitor PS outside the home, in a motor vehicle in particular so if the receiver has such frequencies programmed or the VFO is tuned to one... YOU EES BOOSTEED amigo.
One thing to note, holding an Amateur Radio license has absolutely NOTHING to do with any of this. Showing your ticket to a cop is like offering a lion an apple if you know what I mean.
The laws do NOT differentiate between receiver types, as a matter of fact many are worded as "shortwave receivers" showing how old those laws are and how legislators are totally ignorant as to radio communications in general. This ignorance at all levels makes things tricky at best, don't expect plumbers to know a thing about electricity and lawyers know even less.
One more thing to note, law enforcement is VERY scanner unfriendly as if you don't already know. Legal or not they can make your life miserable so better safe than sorry, leave it home and find something better to do in your travels like counting bottles of beer in the wall.