Being observant isn’t being nosy. Nosy wants the story. Observant wants to help.

The difference is what you do with what you notice. Both people see that somebody has been crying in the stairwell; one goes to tell three friends and one goes and sits down next to them. The noticing is identical, and the whole moral weight sits in the next thirty seconds.

So when you spot something about a person, ask what it is for before you say anything. If the answer is that it would make a good thing to pass on, keep it. If the answer is that they could use something, do that quietly instead, and do not mention it to anybody afterwards.