I do the same thing. In my case it's simply because I'm a serious car enthusiast that dislikes the way a front lic plate obscures the beauty of the front end. Both my German & Italian cars have such gorgeous styling I can't bear to muck it up with plates.
Why the plate frame?
I've found that if I have them install a plain chrome or black plate frame (depending on car color) I get stopped less. That's purely a trial and error result. Just guessing that if they don't see a plate frame it may be mistaken as stolen when viewed at a glance, before they decide if they are going to pull me over.
Don't hate on us just because we can afford great cars. It takes a lot of work & responsibility which is no secret. Just common sense. Its an earned luxury.
LOL. This coming from the guy with a Bugs Bunny rainbow avatar...