Copper is right the best thing you can do is acknowledge they they are there. A smile, a nod, those count so much.
One memory I'll never forget is when I was in Dallas, not really a good place to be homeless, a really well dressed woman, one of those with the big blonde hair,was on her way into an elite store I was standing at a bus stop. I hadn't eaten in a while and the heat was getting to me, I must had looked pretty bad because out of all the people standing there waiting she stopped looked me in the eye and asked if I was alright. I was so panicky at being singled out but she was so kind. She went in the store and came back out with a bottle of water which tasted like heaven and helped a lot.