I was going to troll and tell you they arent made out of aluminum, then i decided to google it to make sure none of them are aluminum. Turns out most of them are aluminum, maybe all of them. I know my Florida tag was held onto my 74' bmw 2002 with magnets because i didnt have the bracket and refuse to drill a new hole in my car, maybe the vintage tags are steel? Seems like making them out of steel would make them cheaper and easier to mount temporarily.

Dealer plates are on magnets, think they're bolted to some kind of frame first.

4 suction cups doesn't sound strong enough, I'm not seeing how it could fly off and seriously hurt you more than any other object in the car.

I have a KY tag that magnets stick to, but I don't think it works with OH tags.

Thats absurd, I would keep it in the trunk or some shit.