Wow when going through the pictures I didn't notice the plates thing but that is definitely a no-no if you want to stay under the radar. I would not rock that look, but if you continue to do so, atleast write that it is for FE on the cardboard.
That will give an explanation to others looking at your car dumbfounded.
Like others say, that doesn't look to sturdy. It could fly off at any given time. That is a hazard in my book.