Could The Dark Line Around My Friend S Wrist Be A Sign Of Something Concerning?

Hello my friend has a dark line that has formed around her wrist. The line is in full circumference of the wrist and is about 1/16 of an inch thick to 1/8 the line appeared over night and unlike the marks from her hair ties on her wrist this one has not gone away also she doesn t often wear hair ties on her left hand, curious to see what comes of this