Mine is on the back side of my swing arm tag bracket. It is not visible from the rear of the bike and i have never been given any trouble about it. Infact I rode without an inspection sticker on the bike for the first three years i had it, at first because i cut off the mudflap and accidently thru it away and then because i didn't inspect if from 2003 when i purchased it until late last summer. I have never even been asked for insurance when i get pulled over let alone and inspection sticker, most of the time the cops around dallas are just happy that they can see my plate from behind the bike since most of the kids put it up infront of the rear tire where you can barely see it.
I'd just put it where you think it looks the best and not worry about it again.