Truth be told, I can't get into signing all my Christmas cards, "Jesus is the reason for the season" or "Keep the Christ in Christmas." It seems to me that people who worship Jesus are going to do it anyway, and people who don't just find it annoying.
What I find amazing is that the beauty of Christmas crosses belief systems. Even atheists can't be blind to the abundance of joy, giving, awe, and wonder that Christmas brings. The celebration of the birth of the Christ child causes food pantries to be filled, the homeless to have coats, loved ones to be given gifts and adults to celebrate the joy of being a child.
And that is far more powerful than a phrase on a bumper sticker or a sign in the front yard. That is the real, living breathing Christ in Christmas.