'Xmas' is another way saying 'Chirstmas' which is supposed to be more secular than the latter. However, the 'X' part of 'xmas' was used by early Chirstians to identify themselves as a follower of Christ. By marking an 'X', they signified either a safe house, gathering place, or the like. X is the character for the Greek letter "Chi" which was the first letter of Jesus' name in Greek.
To say that xmas may have no religious value today is perhaps true, but ironic becasue xmas and Chirstmas are literally one in the same.