" Some people need a gentle hint"
eyespy is right. I followed the Space Shuttle disaster almost from the outset right here on FR. I was most affected. Yet, at work the next day, one of our tenants had to remind me about the flag. I was very grateful to her and it was lowered immediately.
Your right, sometimes its not intentional.
There is a gigantic one in my hometown in MI in front of a car dealership. I mean it is mammoth. It is flying at half staff and just the sight of it got me going.