Here's more background on X being ancient symbol of Christ. A truly
remarkable thing lost on Christians debating X-MAS taking Christ out
of Christmas. I mentioned it to my 7 year old son and he said "yes Mom
it's because its a cross on its side or like when he fell" He already knows
so much more than me. What will be it like when he's 14 or 24? I spoke
with my kids about that Seasons Greetings is meant to be all inclusive
more than take Christ out of Christmas and my 9 year old daughter
responded "Well that's good because faith should be all in One Mom. It
just angers me that it is not. It is one God it should all be ONE faith"
Wowzer. They are such a pleasure to talk with. Brighter than many
adults for sure. Happy Holidays and er um Merry Christmas too!
"Crux decussata" ("decussated cross") or "St. Andrew's Cross": called "decussated" because it looks like the Roman Numeral "10" (decussis), it is also called St. Andrew's Cross because St. Andrew was supposed to have been crucified on a cross of this shape.
By the Monogram of Christ is ordinarily understood the abbreviation of Christ's name formed by combining the first two letters of the Greek form (see Greek word 1, in table above) thus (see Monogram a); this monogram was also known as the Chrismon. There are, however, besides this type of monogram, two other monograms of Christ -- one of His name, Jesus, the other of both His names together. The most common form (that first alluded to), was adopted by Constantine the Great on his military standards. The monogram of the famous labarum (q. v.), as described by Eusebius (Vita Const., I, xxxi), is that given above. Lactantius (De mont. persec., xliv) describes it as "transversa X littera summo capite circumflexo", a somewhat obscure expression interpreted by Hauck ("Realencyk. für prot. Theol", s. vv. Monogramm Christi) as a X with one of its strokes perpendicular (see Monogram b) and the upper arm of this stroke rounded to form a P (see Monogram c). Many variants of these two forms exist in the monuments of the fourth and fifth centuries. The Greek letters XP combined in a monogram occur on pre-Christian coins (e. g. the Attic tetradrachma and some coins of the Ptolemies), and in some Greek manuscripts of the Christian period they are employed as an abbreviation of such words as (see Greek words 2, 3, 4). Lowrie remarks, however, that when employed as an abbreviation the X stands upright, whereas in the monogram of Christ it lies on its side (see Monogram d), thus appearing more symmetrical. The form (see Monogram c), is of Christian origin; it came into use in the course of the fourth century, and represents a stage in the development of the monogram into the cross