https://en.wikipedia.org/wiki/Pink_triangle

A pink triangle is a symbol for the LGBT community. Initially intended as a badge of shame, it was later reappropriated as a positive symbol of self-identity.

It originated in Nazi Germany in the 1930s and 1940s as one of the Nazi concentration camp badges, distinguishing those imprisoned because they had been identified by authorities as gay men.

In the 1970s, it was revived as a symbol of protest against homophobia, and has since been adopted by the larger LGBT community as a popular symbol of LGBT pride and the LGBT movements and queer liberation movements.