In the olden days, the days of the witch hunts, there was a belief.
When a woman gave herself to the darkness, the Devil arose from Hell, and marked her. The mark of a witch was the devil's mark. It was the colour of strawberries, the shape of a heart, usually found on the left breast.
Old wives' tales, fairystories, you say.
If so, I have escaped the pages of a fairytale.