In ancient times, it was a very feudal society. If a king is partial to a concubine and becomes popular, it is a very bad thing. This concubine will be put in limbo, which is likely to directly implicate her family. This is a very bad omen. Therefore, if the ancient concubines were favored by the emperor and encountered "inconvenience", they would definitely arrange eunuchs in advance so that the eunuchs in charge would not present her brand to the king.
At the same time, if you meet a princess that the king loves very much, then these people will put a little red on the princess's brand, so that the king will understand at a glance and will not turn over her brand. At the same time, in some dynasties, female officials specially recorded this information for inquiry, and then they had a custom that if a concubine came to the moon, she would hang a special lantern on the door. Then the female officer knew what it was like at first sight, reported it to the eunuch in charge, and then marked her own brand with a certain mark, so that there would be no mistakes.
In ancient times, if you were partial to the king in those inconvenient days and then saw the red, it was a very bad thing, so they thought of some ways to solve and prevent such things.