I was raised southern baptist In the south, in the buckle of the bible belt. But again, never have I encountered that kind of thing, and I'm covered in tattoos and piercings.
I don't understand why you need everyone to know you are atheist. You just are. However, tattoos are a personal thing, and I guess if you want everyone to know you are atheist in this tiny, weirdly religious town, you are certainly welcome to it. It seems like you are kind of asking for people to hassle you. I don't understand it at all, but as my Mom always told me, to each their own.