This thing was from the idea of Matsu, the store manager of Blue Lug Yoyogi Park.
It's a reflector that you can "sandwich" on to your bikes.

This is the special traffic safety and crime prevention version!

"自転車盗難警戒中" = "On alert for bike thieves"

They also works as a nice key chain or a safety charm to put on your bags. Try it out!

*The colors of the strings on the tips will all be random.