During Breaking Bad’s run, they had a weekly podcast with the editor (Kelley Dixon) and Vince Gilligan. One of the things that came up in quite a few of those was how much time they spent getting permission from copyright holders to have things in the show. IIRC, they had a team dedicated to just that. Every single picture, every book, every vase, every brand of everything, they had explicit written permission to show. In some cases, where they didn’t even technically need permission (IIRC, they didn’t for things like outdoor graffiti, they’d still get it). They were so used to the copyright holder having some hesitation about it that when people would say ‘you want my artwork on a TV show!? Yes, of course’, they felt the need to explain the show’s premise to make sure the person understood what they were agreeing to’.
I usually see a license plate that looks like a license plate, but painted the same color as the car. That way you don’t have a big empty license plate holder area, but you also don’t have a big reflective license plate drawing your eye away from the car. It’s probably cheaper than fabricating a one-off bumper without the license plate holder on it just for a few commercials.