Smiles from strangers

Recently I have noticed that quite a few people will smile at me when I'm out and about. Today, as I left the house to meet with a friend, I was crossing a pedestrian bridge near where I live, and once again, it happened. This young girl looked at me and smiled. I smiled back, of course, but this time I took notice and started thinking about all these strangers who recently have randomly smiled at me. After all, this is London, one of the biggest cities in the world, I don't really expect a lot of friendliness.

I wondered if it was because I was out in the middle of the morning, instead of the rush hour. Are people that are out and about outside of rush hours a bit more friendly? It's plausible. I certainly feel much happier these days when my day is not governed by a strict 9-5.
Could it be that because I am happier, more relaxed and walking a lot slower than I have ever done, I now have time to notice people and they notice me more? Or could it be that I emanate more of this contentment? 

I still don't know the answer to it and I will continue smiling to strangers in this big city and will be grateful when I get a smile back. 
Life is not all smiles, contentment and happy thoughts, but when these do happen, it makes a difference.

What have you not been noticing? Do you ever smile at strangers?