What is a king's umbrella?

The traditional duet "Echo Story" tells a story: Zhang Tingxiu and his son fled from Hongtong County to Suzhou City to work as carpenters for the renovated Wang Fu. Wang Sanlao, the supervisor, will visit fortune-teller, saying that Zhang Tingxiu has a "king umbrella" on his head and will be a big official in the future.

I don't blame the pink one. I do have a faint red umbrella birthmark from forehead to forehead. You can't tell without looking carefully.

"Peach, you don't understand. It's called the king's umbrella. In the future, this little scholar will be a big official. " Peach mother said seriously.

To sum up, the king umbrella should be something similar to a birthmark. According to feudal superstition, this is a good sign for being an official.