Saint GPT :

The lambda symbol was first adopted as a gay symbol in 1970 by the New York Gay Activists Alliance and became the symbol of their growing movement of gay liberation.
In 1974, the International Gay Rights Congress held in Edinburgh, Scotland adopted the lambda as their symbol for lesbian and gay rights, making it internationally popular.

Initially, the lambda had a fairly militant connotation, but today it generally denotes the shared concerns of lesbians and gay men.
It is used by both gay men and lesbians in the LGBTQ community.

The lambda symbol has been incorporated into various fields including mathematics, science, and engineering, and has also gained popularity in the science fiction genre.

Lambda Legal and the American Lambda Literary Foundation derive their names from this symbol.

https://www.crwflags.com/fotw/flags/qq-lbd.html