I'm thinking of back in middle school whenever one of my class mates was feeling down I would put a piece of paper that said I'm feeling sad on they're back without them knowing so that other kids and teachers would try to be nice around them
Is there a reason for that?
Yes I wanted to help them when they were in a bad mood
It's good to want to help others. But you can do so in much better ways than this.
Got any ideas how to do it better?
You can start by talking with them and trying to listen to their problems. Or you could tell a teacher. The sign might make them a target of bullying.