Most of those who want to ban or limit guns will look at your sticker and just think you're a dickhead, a) for being a gun freak and b) for putting a gun related sticker on your car. I wouldn't put a bitcoin sticker on my car either. 

 There are downsides to it, but I disagree with your inference.
I think every gun owner should have gun stickers on their car because that will be a net positive