Clues to know if someone is self harming, please?!

Those are all possibilities. Try confronting the person you are concerned about, if they question you don't answer.

Tell them that you are there for them and that they will always get support from you. Don't let them continue the behaviour, talk to a trusted adult if they won't get help.

Of course, if someone is doing all of the above, they still might not be self-harming.