http://urbanvelo.org/share-the-road-is-this-a-positive-message-for-cycling/
“The sign’s literal meaning is: Caution! You might encounter a person riding a bicycle on this road…This sign inadvertently reinforces the idea that bicycling is dangerous and thereby discourages people who do not currently bike on the streets from ever doing so….To many motorists it means: Cars have the right of way. Bikes have to move over and let me pass. Bikes are supposed to share the road. In fact, I have heard of several instances in which, after a car/bike crash, the motorist proclaimed: “He didn’t get out of my way! He wasn’t sharing the road!””
Read on
The author does bring up the good point that the Share the Road campaign isn’t easily interpreted and may not even be aligned with the message cycling advocates want to portray.