I'm an NRA member, but do not display the NRA (or any other gun related) sticker on my car. My reason has more to do with advertising that I may have a gun locked up in my car. I might as well put a sticker on there that says: "I have lots of silver bars locked up inside".
When appropriate, I let people know that I am a member of the NRA and that I like to collect and shoot guns. But, this really isn't a big deal in the South.