BikeTV has a short video showing the installation of "sharrows" in San Francisco. Sharrows are directional indicators that are used when bicycles and motor vehicles share the lane. They give the bicyclist an indication of where to ride on the roadway. They are most typically used on roads that have bicycle lanes in those spots where the bicycle lane disappears momentarily. I rode several streets in San Francisco last fall that had these markings and they work very well.