Bicyclists have to survive in a harrowing world: roads designed for and dominated by cars, against which they would lose in almost any accident. Designer Peter Miller realized that they need a way to notify bike-dangerous drivers of their behavior, and something better than shouting or dinging a little bell. His solution: the magnetic Yellow Card, which can be tossed by a biker onto the offending vehicle. It's quite clever, since (as the card itself points out) "it can neither damage your automobile, nor affix itself to rubber or glass and will therefore not affect your driving." It would be a whole separate issue to study the actual reactions of drivers when they get around to reading these, though - perhaps they'd be more angry than apologetic when faced with these cards instead of a face-to-face confrontation. But the concept is certainly intriguing!