X is used for "cross" on traffic signs. Not a religious symbol it is the intersection or "crossing" point. Sign examples are

PED XING (PEDESTRIAN CROSSING)
RAILWAY XING
DEER XING
ETC.

There is a story that the "Cross" in Crossfire is symbolized on the side of the car where the two horizontal planes intesect (cross) on the door forming a X (cross).