I've always found the "Keep Christ in Christmas" signs to be a little weird. They seem more like political campaign signs than proselytizing. They also reveal an ignorance of the actual origin of Christmas traditions.
My attitude may have been shaped by the fact that, in our neighborhood, the guy who put out the KCiC sign every year was the same one who spent the summer telling all of his neighbors when and how they should mow their lawn and tend their garden (he always had an emphatic opinion about home repair projects, too).
For the Christmas Originalists, Heathens, Secular Humanists and ancient history buffs out there, here are some fun alternative holiday signs that you can print out and display if you are so inclined.