According to Norman F. Gorny (2016, p.5):
Another mark, though it is often erroneously called a crescent, is the nail mark, #30002;#25991; ji#257;wén. This looks like the mark of an actual finger nail. Nail marks are probably a type of control mark, but their appearance is sporadic and inconsistent and does not have varietal significance. Do not confuse the nail mark with the crescent.
https://www.google.co.uk/books/edit...c=frontcover
Another mark, though it is often erroneously called a crescent, is the nail mark, #30002;#25991; ji#257;wén. This looks like the mark of an actual finger nail. Nail marks are probably a type of control mark, but their appearance is sporadic and inconsistent and does not have varietal significance. Do not confuse the nail mark with the crescent.
https://www.google.co.uk/books/edit...c=frontcover