I went 3 years without a front license plate on my s2000 and 1 year on my RX-8. I did get pulled over once in the RX-8 by a highway trooper on my way back from san antonio but the car was fairly new and he let me go with a warning since I told him my dealer hadn't gotten the bracket for me yet.
Now that I have the Z the bracket is there and I might just keep it. I figure I got away with it for about 4 years and I might as well put it on since the bracket is already drilled into my bumper
