Handkerchief code (English Wikipedia)

Reilly, Andrew; Saethre, Eirik J. (2013-10-01). "The hankie code revisited: From function to fashion". Critical Studies in Men's Fashion. 1: 69–78. doi:10.1386/csmf.1.1.69_1.
Filice, Eric; Raffoul, Amanda; Meyer, Samantha B.; Neiterman, Elena (2019-07-05). "The Impact of Social Media on Body Image Perceptions and Bodily Practices among Gay, Bisexual, and Other Men Who Have Sex with Men: A Critical Review of the Literature and Extension of Theory". Sex Roles. 82 (7–8): 387–410. doi:10.1007/s11199-019-01063-7. ISSN 1573-2762. S2CID 198629523.

hornet.com (Global: low place; English: low place)

Fischer, Hal (1977). Gay Semiotics ♂. San Francisco: NFS Press. ISBN 0-917986-03-2. Archived from the original on 2019-10-18. Retrieved 2017-06-23. In San Francisco, the signs began appearing around 1971. The Trading Post, a department store specializing in erotic merchandise, began promoting handkerchiefs in the store and printing cards with their meanings. The red and blue handkerchiefs and their significance were already in existence, and meanings were assigned to other colors as well.

Filice, Eric; Raffoul, Amanda; Meyer, Samantha B.; Neiterman, Elena (2019-07-05). "The Impact of Social Media on Body Image Perceptions and Bodily Practices among Gay, Bisexual, and Other Men Who Have Sex with Men: A Critical Review of the Literature and Extension of Theory". Sex Roles. 82 (7–8): 387–410. doi:10.1007/s11199-019-01063-7. ISSN 1573-2762. S2CID 198629523.

Kacala, Alexander (April 25, 2019). "The Handkerchief Code, According to 'Bob Damron's Address Book' in 1980". The Saint Foundation. The Saint. Retrieved March 30, 2021.

Fischer, Hal (1977). Gay Semiotics ♂. San Francisco: NFS Press. ISBN 0-917986-03-2. Archived from the original on 2019-10-18. Retrieved 2017-06-23. In San Francisco, the signs began appearing around 1971. The Trading Post, a department store specializing in erotic merchandise, began promoting handkerchiefs in the store and printing cards with their meanings. The red and blue handkerchiefs and their significance were already in existence, and meanings were assigned to other colors as well.

Filice, Eric; Raffoul, Amanda; Meyer, Samantha B.; Neiterman, Elena (2019-07-05). "The Impact of Social Media on Body Image Perceptions and Bodily Practices among Gay, Bisexual, and Other Men Who Have Sex with Men: A Critical Review of the Literature and Extension of Theory". Sex Roles. 82 (7–8): 387–410. doi:10.1007/s11199-019-01063-7. ISSN 1573-2762. S2CID 198629523.