An article shared by President Trump featured an upside-down pink triangle, crossed out by a red "no" symbol. Why LGBTQ+ and Jewish advocates are alarmed.

San Francisco police have arrested a man accused of defacing the famed Pink Triangle, a symbol of LGBTQ+ rights that is installed annually during Pride Month on top of the city's landmark Twin Peaks.

The triangle isn't an arbitrary symbol; Nazi Germany marked gay men with a pink triangle to identify them. At least 15,000 gay men were sent to concentration camps, and 60 percent of them were killed.

The pink triangle was used by LGBTQ+ activists as early as the 1960s, but it became more widely adopted during the 1980s as a symbol of resistance in response to the AIDs epidemic.

An article shared by President Trump featured an upside-down pink triangle, crossed out by a red "no" symbol. Why LGBTQ+ and Jewish advocates are alarmed.