Any visible gun may be in violation of State law, ymmv. In MO, long arms have to be unloaded with ammo separate, in a case out of reach, for example. That was passed long ago thru the excuse that it would stop road hunters whipping out a loaded deer rifle to take shots across an open road at game.
Now, who would do that? Well, it was happening, in MO, with arrests of locals who weren't always hunting during season, and the MDC was using a remote control Bambi as bait.
Another issue is that vehicles that may appear "gun-ish" are targeted for theft, glass is broken, which isn't cheap, guns stolen. The primary source of stolen firearms in major metros is theft, and the biggest growing category is from trucks and cars. As we improve difficulty in getting into vehicles, and securing items like stereos, thieves have moved to personal electronics, sporting goods, and guns for quick sale. And there are more thieves as drug use grows.
Under CCW laws in some states, exposed firearms are considered not being concealed. Ooops - open display may fall under some kind of brandishing interpretation, and definitely "not concealed" means "illegal" under their view. Closely examine your states CCW provisions, check their FAQ's, and see what you can and cannot do. That can even be different 10 miles outside a metro in rural parts where inside the ring it's a different anti gun application. And when you cross from one to the other? Good luck defining that, they don't paint color coded stripes on the road. We are lucky to even get a sign near a school, and that is a whole nuther set of rules.
Then there is the issue of does your state include parking, or not? Take an example, MO at one time was NO CCW on church property (and who gave the state any authority over the church? but moving on) yet TN policy says it's up to the church, leave us out of it. Read their signs or policy. An interesting wrinkle in that is that despite MO state law, churches still allowed CCW, had armed ushers, and my LEO CCW course instructors spoke on how they carried in church during the service. Their implicit statement was "ignore the law." OK, you leave the gun in the vehicle during service, but, still on the property, your car is damaged in an high speed chase thru the grounds and it falls out of the door pocket visible to the officers on the scene. Bingo.
Now we get into officer discretion. Good luck as it's a roulette wheel of dozens of policies, statutes and what constitutes a "reasonable" perspective.
For the most part, gun ON the individual is much safer than rusted gun sliding around in a locked case with ammo corroded in the chamber. A motor vehicle is a 4500 pound chunk of metal with poor seals - its not a submarine - and humidity can and will enter the interior, temperature changes occur twice daily, a cold gun sitting in a saune of hot wet air will condense moisture on all the surfaces on it, 3D, every one. It should be treated as a marine grade environment. Guns rust in vehicles and need triple the maintenance of one carried. Even with that, they speckle, lose finish, internally corrode, ammo deteriorates (temps to 145F are common in the summer.)
Plus it's another $450 up of diverted money taken from discretionary money and with inflation ramping up severely - gas last year was $1 and change, this year some areas are already seeing $3 and metros are quickly closing on $5. If you have to drive to work a lot, you may need that $450 for future fuel increases. Or, worse, you are fired for not complying with new company policies that hundreds of corporations and tens of thousands of businesses are considering between now and Nov 1.
What is nice, is that it's up to the individual. I just carry in the car when I need to, same guns nothing special or dedicated and no risk of theft unattended. I only put my AR15 pistol in it - unloaded cased - when hunting during alternative methods season. Doesn't mean I won't carry a 9mm in a shoulder holster, too, which I can do at any time. Having had numerous things stolen out of vehicles over the years repeatedly, I won't leave even more desireable and legally difficult things in a car unattended. Tools, knives, insurance papers, change from the ash tray, whatever, a neighbor kid sneaking around after dark on a scavenger hunt is a resourceful thief, and I'm not giving them loaded guns on top of the reefer they inhaled to work up their courage.
I live in what is considered a "good" suburban area. It was much worse in the last one - wheels batteries drunk drivers hitting multiple cars theft rampant. It was relatively better there than the "bad" ones a few blocks away. I upgraded from weekly to yearly, is all.