From wikipedia:

The pink triangle (German: Rosa Winkel) was one of the Nazi concentration camp badges, used by the Nazis to identify male prisoners in concentration camps who were sent there because of their homosexuality. Every prisoner had to wear a triangle on his or her jacket, the color of which was to categorize him or her according “to his kind.” Jews had to wear the yellow badge (in addition to any other badge representing other reasons for incarceration), and “anti-social individuals” (which included vagrants and “work shy” individuals) the black triangle.

The inverted pink triangle, originally intended as a badge of shame, has become an international symbol of gay pride and the gay rights movement, and is second in popularity only to the rainbow flag.

By the end of the 1970s, the pink triangle was adopted as a symbol for gay rights protest. Some academics have linked the reclamation of the symbol with the publication, in the early 1970s, of concentration camp survivor Heinz Heger‘s memoir, Men with the pink triangle.

The pink triangle is the basis of the design of the Homomonument in Amsterdam, the Gay and Lesbian Holocaust Memorial in Sydney, the Pink Triangle Park in the Castro neighborhood of San Francisco and the huge one-acre Pink Triangle on Twin Peaks that is displayed every year during San Francisco Pride weekend in San Francisco.

Reclaiming a previously offensive term, the gay areas of both Newcastle upon Tyne, England and Edinburgh, Scotland are colloquially known as the Pink Triangles on account of their approximate shapes.

3.75″ Round