I've heard that the
X symbolises a normally puckered and tight anal sphincter of someone who has the True Christian™ attitude to the one way nature of the orifice.
The
D, however, symbolises the floppy and distended nature of the anally ravaged sodomite's sphincter.
It is therefore a "celebration" of the inevitable journey of the godless from anal virginity to outright wanton sodomy. And it is being flaunted right before our very eyes all over the interwebs!