A red string around your wrist is worn to denote you have embraced anorexia. Ana-Mia. The dragonfly also denotes the same and both a red string bracelet and dragonfly are used by anorexics to identify each other.
Red strings have nothing to do with masonry.
https://eatingdisordersolutions.com/the-dangers-of-the-red-bracelet/#:~:text=You%20see%2C%20the%20red%20bracelet,but%20not%20yet%20overcome%20it.