Our local atheist group wears bright blue t-shirts with "Ask an Atheist" boldly printed front and back while we walk in pairs at events, the mall, etc. Our purpose is visibility and availability to answer questions. We've done this 3 months now, with generally supportive response. The visibility is working.
Please see http://outatheist.info for more info and photos. You will find resources in case you might consider starting such a project in your area. It's very simple, yet highly effective and rewarding. Check out the small website to see what we've done, and to see some tips if you might consider the same for your local community.
I think it's the most important thing we atheists can do right now in this country. Not all atheists are prepared to go out visibly, so I feel it is more important for those of us who can to do so. But, then, I've always been a risk-taker.
Often we have tag-along atheists who do not answer questions, but walk with us in support. In fact, we even have had believers walk along with us in support.
It's working. It's what we need, especially now in America. Join us?