I saw one of the best ever motorcycle safety posters on a billboard in Switzerland a couple of years ago. It was in negative color, black/red, showing a bike coming head on at the camera, leaning well over, rider knee on the road, obviously going really fast. The caption underneath read, in big letters (in French) "t'es sur?" which in English means: "you sure?". So it didn't mean go slow, it meant go fast if you want but make sure you know it's safe. It really stayed in mind.
The same road safety campaign had a poster reading in big letters: POLICE OFFICERS SLEEP TOO and in small letters below: but not all at the same time!