Some states in the US have license plates with a "Share the Road" message and design for for bike concious drivers to put on their cars. Tokyo needs to get the same message accross and educate to the drivers that bikes have their spot on the road, and are vehicles that belong on the road, not just the sidewalks.
Though this is one good way to do so, the Japanese traffic authorities needs to first authorize designed license plates :- (

• BikePortland.org : "Will Oregon Get a Share the Road Llicense Plate?"