This zone, where there is, as James Madison said, a "line of separation between religion and the Civil authorities," falls within the sphere of my scholarly specialty and citizen interest; as such, I should declare myself. I think Christians and other religious people have a right to festoon any and all public places that are not governmentally-connected. Malls, galleries, markets, and lawns, which are open spaces and facilitate gatherings of many sorts, are appropriate places for symbols and signs.
Similarly, I am in the camp of those who believe that alert and aware schools can teach and exemplify the difference between "performance" and "worship," so that madrigal groups do not have to sing only bad secular stuff, but also high-art works of religions--including appropriately chosen Christmas songs in season. Such schools should also teach "about" religion, though they should not teach that a particular faith is "the truth about life."
Having muddied and messed up the line, it's time to come to the point. This year among the most noticed controversy has to do with the Macy's department store in New York, which has removed the word "Christmas" from its objects and transactions. This is a test case for a thesis I would propose. My thesis: most of these December fights are not about religion and religious faith--there are plenty of closets and chambers (Matthew 5:6) for nurture of personal faith, and steeples, domes, towers, and tent tops under which the public can gather for worship.
Instead, they are about who belongs and who doesn't, whose space this is and whose it is not.
How about this approach: religious people express themselves openly wherever the context is one of persuasion, not coercion or governmental privileging, aegis, or auspices. Where does Macy's come in? I suggest that court decisions inhibiting formal prayer and particular symbolism reflect a reality in which businesses, advertisers, markets, and citizenries already live.
Macy's does not "do" Christ in Christmas because it is sensitive to diversity and does not want to alienate and lose sales. People who don't like such a policy can shop elsewhere, and boycott if they wish. They do not boycott because not enough in their constituencies have the courage of their convictions. So they ask for "the sword," that is, "the state" to do what they, as individuals and religious groups, have not succeeded in doing nor even want to do.
Macy's is responsive to customers and the message of non-customers, as are all merchants and advertisers. Christians can let their actions serve as witnesses and persuaders.