A stopper club is a club.
The members always have to carry a plug.
When 2 members meet,
they show the plug to each other.
If a member does not carry a plug,
the member has to pay a fine.
Words with same meanings
The stopper club uses the fine money to purchase beer,
for the next club meeting.
Or they do charities with the fine money.
Most of the stopper clubs are in Germany.
In Bavaria there are more than 100 stopper clubs.