Most states allow it if you have a ham license or special permission
This is wrong. Most states don't restrict your right to have and operate your own property in a vehicle as long as you aren't falling afoul of distracted driving laws or hands-free laws.
There are a few states with laws on the books that do restrict this, however.
Kentucky statute 432.570 says no portable scanners or radios, whether or not in vehicle, capable of receiving police frequencies. Also written in this section if a provision that if a frequency could at some time in the future possibly be assigned to police, then that is also forbidden. Strictly interpreted, this restricts all radio receivers? There is an exception for use in your own home.
Florida statute 843.16 states you cannot have radio receiver "adjusted or tuned" to receive police or fire frequencies. I would assume this covers programmed frequencies to be safe, but a strict interpretation could also allow a programmed scanner that is not currently on police or fire frequencies. There is no mention of the device being capable of receiving those frequencies, however. Interestingly, the law as written would allow a scanner tuned to out of state police frequencies, as long as there are no in-state allocations at the same frequency. Exceptions for "amateur radio operator" and "recognized" news agencies exist, among others.
New York section 397 states no receiver capable of receiving police frequencies are allowed to "be equipped" in a motor vehicle. Exception for amateur radio operator, permit may be required even so, opinions seem mixed.
Minnesota statute 299C.37 states you may not "equip" a vehicle with a device capable of receiving police "emergency frequencies". Exception for amateur radio operator, unless you have committed a violent crime.
Indiana use is illegal while mobile, including on foot. I don't care enough about Indiana to look it up futher.
https://www.zipscanners.com/blogs/learn/are-police-scanners-legal
There are also laws in a few more states that make it illegal to use a scanner in the commission of a crime. Whether or not a car is involved can vary, also.
TL;DR A few states restrict your ability to operate a scanner in a car, only Kentucky and possibly New York don't have exceptions for ham licensees. I'm sure my Kentucky friends would be very interested to learn this and then completely ignore it.
Edit: Found what looks to be a comprehensive overview on the subject.
Mobile Scanner & RADAR-Detector Laws In The US - US Scanner Laws