Apache Knuckle Duster
This thing is apparently called an Apache Knuckle Duster:
In the early 1900’s France went through a period of unrest in which the lower class “Apache” gangs would accost the middle-class homemakers, a group who’d been brought up to avoid violence and were thus entirely unprepared. The gangs often carried combination weapons such as this, not something that could be taken seriously by anyone with a proper gun or blade, but a real enough threat to those who couldn’t defend themselves.
In the end though, the solution was Jiu Jitsu.