Smile to yourself, don't smile to others, apart from children, smile to them, for they will appreciate it and understand. But don't smile to their mothers and fathers. They will think you are weird.
Don't smile to strangers, they will ignore you, or will take it as your weakness and will dare to approach you and ask for money or a cigarette.
Smile to yourself, to the face in the mirror, you will feel safe, you will feel like a winner!