Pick and Mix Hankies | Wikipedia | 14236
The handkerchief code is a color-coded system which is widely used in the gay subculture to indicate sexual identity. There is no single set code of colours and what they mean. The hankies are worn in the back pocket or, if there is no back pocket, threaded through the belt. The left side is usually used to indicate active and the right side for passive.
The wearing of various colored bandanas around the neck was common in the mid- and late-nineteenth century among cowboys, steam railroad engineers, and miners in the Western United States. There are photographs of men in the Californian Gold Rush using the hanky code (in their back pockets).