You can make it effectively invisible if you print the noise in ink only visible to UV cameras and even if you use black, the individual features are smaller than a fingernail so it would be hard to see.

The law makes it illegal to put anything on the plate at all, here's an example from FL:

A person may not alter the original appearance of a vehicle registration certificate, license plate, temporary license plate, mobile home sticker, or validation sticker issued for and assigned to a motor vehicle or mobile home, whether by mutilation, alteration, defacement, or change of color or in any other manner. A person may not apply or attach a substance, reflective matter, illuminated device, spray, coating, covering, or other material onto or around any license plate which interferes with the legibility, angular visibility, or detectability of any feature or detail on the license plate or interferes with the ability to record any feature or detail on the license plate. A person who knowingly violates this section commits a misdemeanor of the second degree,

It would be hard to disrupt the OCR from outside of the plate area.

You could break the segmentation, the process where it draws a box around your plate and sends the image inside of the box to be OCRd by making every other surface of your vehicle detect as a license plate using the same invisible marks. I imagine you could also print a bumper sticker with noise to look maximally like a license plate and put it near your real plate to achieve the same outcome.

If you wanted more active measures you could use high lumen UV floodlights next to your plate, it would overload the sensors so they couldn't get an image at all. The light would be invisible to human eyes but blinding to anyone using a UV sensitive device. I believe this is fine in any state as most states only restrict your ability to install blue lights to avoid confusion with emergency services.