For reasons that should be obvious, signs placed in sight of elevated roadways tend to stay up longer than most. This fence, near Thurgood Marshall High School in SF, is a favorite. Although physically no more than fifty feet from traffic, it takes miles and miles of driving, (and if you don't know precisely how to get there, a hell of a lot of hunting around) to actually reach. As this is one of the more sparsely-travelled sections of the 280, signs placed here aren't seen by too many more than seventy-five to a hundred thousand people per day. Still though, it adds up. The sign above has been up for three days now.
FB - 333
USA - 350