black triangle
1. An unidentified flying object (popularly known as a UFO) in the shape of a dark triangle, typically with points of light in each corner. I know you think I'm crazy, but every spring, I see those black triangles appearing over my corn fields at night!
2. In Nazi Germany, a badge assigned to concentration camp inmates considered "asocial" or mentally unfit for work. Her clinical depression, which was vilified by the Nazis, meant she had to wear a black triangle in the concentration camp.