There must be some skill and judgement involved in deciding exactly where to place these notices. I would agree that they have to be prominent, but when I spotted a dozen notices on a long fence, I just had to snap a couple of pictures. Click on the images to enlarge.
Things are getting worse when a painter paints around the “Wet Paint” notices!
One is compelled to suppose that when the paint has dried, the “Wet Paint” notices are removed from the unpainted area, and stuck to the new paintwork to alert people to the fact that small areas may still be wet!