I don't know about Florida .. but in Chicago anything covering your plate is illegal. Reason being is because of speed cameras and red light cameras.
Anything covering is assumes the license plate cover is tampered with. So when they take pics the plate wont be exposed.

So I would assume in Florida too.

 

I found THIS on officer.com. a Cop website where they argue back and forth about traffic stops and whatnot...

Florida law is really simple and clear on this one:

320.061
Unlawful to alter motor vehicle registration certificates, license plates, mobile home stickers, or validation stickers or to obscure license plates; penalty.

—No person shall alter the original appearance of any registration license plate, mobile home sticker, validation sticker, or vehicle registration certificate issued for and assigned to any motor vehicle or mobile home, whether by mutilation, alteration, defacement, or change of color or in any other manner. No person shall apply or attach any substance, reflective matter, illuminated device, spray, coating, covering, or other material onto or around any license plate that 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. Any person who violates this section commits a noncriminal traffic infraction, punishable as a moving violation as provided in chapter 318.

Simple for us simple folks in FLorida..

SO- to answer your question, it IS illegal, although I don't know HOW they could PROVE you HAD used the spray... the Cover- that is an easy one to spot. BUT- the spray is clear and only with a flash (Or a cop's high beams maybe) could they tell that it was on the plate. Hope this helps.
I live in an area where I see on a DAILY basis the dang flashes go off if a person stops SLOWLY, or goes about an inch further than the cameras "acceptable range". If a police officer was there- would have been no ticket. BUT- the light flashes ALL the time and the people ARE stopping.
I AM getting some, JUST to protect myself.

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