Don't hide. If people ask you, tell them.

Act as if there's nothing wrong with atheism, which there isn't. Be yourself.

Religion and politics does not belong in the work place, unless that workplace is of one of religion and or politics (and if so, you have a very unfortunate workplace).

I used to live in Oklahoma and I would try to keep your atheism private in a school setting, even though they can't afford to lose anymore teachers. A few years ago in my Dad's town (Okemah) a teacher made national news when she sent home some literature with a young left handed student informing his parents that being left handed was the devils work, in an effort to get him to write with his right hand. So there's a sample of the mindset in that state, and of course the teacher kept her job.

First - in a professional work environment there is no place for political or religious discussion.
But. People being what they are, choose your battles.

Depends on situation as it could cost you job or promotion if you not the boss.

That's a good policy, my friend. I'm the same way. My work place is overrun with the Mormon Mafia. I don't like their ideology but I like them as colleagues.

I curb my atheism at work. My employer says the group is very religious so my take on it all at work is that I once studied for the ministry but today I am not religious. That's about where I leave it just to play it safe.

If someone opens Pandora’s Box, that’s their fault.

I'm the same, I work in a science museum in South Carolina. I often get questions like "where does god live" when teaching astronomy.

I just point out we have no scientific answers, haven't found a location. I avoid "I think" or "I believe" statements and just gives the facts we know and highlight what we don't know.

I tend to steer conversations away from religion and politics in mixed company in most situations, including work. But most who know me know I'm not religious. I just state it that way and nothing else.
That said, one day I sat down at my computer terminal and noticed a very religious employee had left a bible scripture in an open daily notes window. The previous dispatcher told me this person had a regular habit of this. I made a huge deal out of it. Straight to the director. I'm not putting up with that crap when I feel I need to be discreet about my own beliefs, or lack thereof in order to peacefully exist in the workplace. It never happened again.

I don't hide it, but I also don't flaunt it. We are still a minority and one that every other minority feels fine discriminating against. It could very well hurt your career if you are too in your face with it.