This is an english summary of my thesis Classifying Galaxies, Gays and Geeks - Signature Codes in Usenet Postings, written in 2005. See also: At least 80 signature codes and Topics in different Geek Code versions.
The idea of signature codes in Usenet postings was introduced in 1990, when Bob Donahue and Jeff Stoner published a version of the Natural Bears Classification System - A classification system for bears, and bear-like men in the newsgroup soc.motss, a forum for gay-related discussion. The signature code was devised in late 1989 and used at first only on the Bears Mailing List.
During the following years, several similar codes emerged. However, they were still used only by the lesbian-bisexual-gay-transgender community and mainly in newsgroups soc.motss and soc.bi (a newsgroup for discussion related to bisexuality).
Things changed in 1993, when Robert Hayden developed the Geek Code. It was first released in soc.bi, but soon cross posted to several newsgroups of geeky origin (i.e. alt.geek, comp.os.linux, rec.arts.startrek.misc and rec.games.frp.misc and the like). The new code appealed to a much wider audience than its predecessors and was an instant hit.
Soon there were codes being generated everywhere. Codes for My Little Pony collectors, Macintosh users, jugglers, scouts, pets and for fans of various TV series and bands. There are at least 80 different signature codes.
A notable amount of codes have disappeared from the web since the 1990's. As the WWW gained popularity, fewer and fewer signature code descriptions were posted to newsgroups. The most important source in my research was the Google Groups' archive of Usenet postings, dating all the way to 1981. Another important tool was Internet Archive's "Wayback Machine", which allows access to archived versions of web sites dating from 1996.