What is the large silver "button" used to fasten rear Japanese license plate on vehicles called?


One of the two screws is larger and has a prefectural seal affixed to it. I
want to determine its purpose and name.




This seal is called 封印【ふういん】.

From [JAF](http://www.jaf.or.jp/qa/car/registration/07.htm) (the Japan
Automobile Federation):

> 封印の目的はナンバープレートの取り外しを防止するとともに、車両の盗難犯罪を防ぐ重要な役割があります。
>
> (Roughly, _The purpose of the seal is to block the detaching of the licence
> plate as well as being a preventative measure against motor vehicle theft._
> )




This seal is called 封印【ふういん】.

From [JAF](http://www.jaf.or.jp/qa/car/registration/07.htm) (the Japan
Automobile Federation):

> 封印の目的はナンバープレートの取り外しを防止するとともに、車両の盗難犯罪を防ぐ重要な役割があります。
>
> (Roughly, _The purpose of the seal is to block the detaching of the licence
> plate as well as being a preventative measure against motor vehicle theft._
> )

