What are some ways people express their mental illnesses?

This question was inspired by a post that I saw saying that people that dye their hair bright unnatural colors can show they are mentally ill which I found stupid but it did make me wonder, that there must be ways people with mental illnesses would express themselves so what are actual signs or ways people with mental illnesses would unknowingly express themselves. Which even tho it's possible to do through fashion, fashion is a way to express yourself in general so it's inaccurate to only assume that their expressiveness is coming from a mental illness when it can be from creativity as well. ๐Ÿค”
What are some ways people express their mental illnesses?
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