Tens of thousands of lesbian and gay people were "exterminated" by the Third Reich. A pink triangle on homosexual men was used by the Nazis to identify and persecute gay men because of their sexual orientation. The pink triangle was reclaimed by the gay community in the 1970s because it was easily identifiable. In the 1980s ACT UP used the triangle with the point facing up to draw attention to the "holocaust" which AIDS represented to gay male communities.
This is one of many SymbolsOfPride.