red triangle

Nazi concentration camp badges, primarily triangles, were part of the system of identification in Nazi camps. They were used in the concentration camps in the Nazi-occupied countries to identify the reason the prisoners had been placed there. The triangles were made of fabric and were sewn on jackets and trousers of the prisoners. These mandatory badges of shame had specific meanings indicated by their colour and shape. Such emblems helped guards assign tasks to the detainees. For example, a guard at a glance could see if someone were a convicted criminal (green patch) and thus likely of a tough temperament suitable for kapo duty.
Someone with an escape suspect mark usually would not be assigned to work squads operating outside the camp fence. Someone wearing an F could be called upon to help translate guards' spoken instructions to a trainload of new arrivals from France. Some historical monuments quote the badge-imagery, with the use of a triangle being a sort of visual shorthand to symbolize all camp victims.
The modern-day use of a pink triangle emblem to symbolize gay rights is a response to the camp identification patches.

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