守宮砂 is basically a virginity mark.
It is occult witch doctor nonsense, but I do know the legend about how it was done.
“A lizard, sometimes referred to by its other name 守宮 (palace guardian), was raised with a diet containing cinnabar. Eventually, the lizard will turn red. The lizard is then killed and ground to a red ink. Upon spotting a virgin in the arm with this ink it becomes a mark of virginity. If the woman loses her virginity, this mark will disappear.”
Does it work?
I am sure anyone with some understanding of modern science would know it’s absolute nonsense. It is however occasionally used in Chinese wuxia or fantasy novel, but that’s why you shouldn’t take fiction as facts.
