When I see graffiti or someone's mark left in a public place, it reminds me that the person that left it and those of us that see what remains are joined together by our response to that art. That is part of what a community is. Experiencing the sights and sounds of a city, or a commute with the people around you whether you know them by name or not.
When I see funny as hell things like what this website shows, I feel this sentiment even more. Some people are so damn funny and sneaky clever.