It was cold in the Manger and Baby Jesus was shivering and fussing.
Mary asked the stable animals to move in closer to provide more warmth. A tabby cat jumped into the manger and curled up beside the Baby Jesus who settled down and fell asleep.
In gratitude Mary bestowed her initial M on the tabby's forehead.
To this day every Tabby cat has a notable M on their forehead.
This is a true story, I don't care what Father Anonymous says.