According to Merriam-Webster dictionary, "anon" means "soon" or "presently." It can also be an abbreviation for "anonymous."
In the earliest form of the word, "anon" meant "at once." According to the Online Etymology Dictionary, it is from the Old English words "on an," which turned into "anon" by the late Old English period. By the 1520s, the word had been corrupted to mean "soon" instead of "at once." In either sense, it is an an adverb.
"Anon." as an abbreviation is often signed to anonymous creative works, particularly in older writings. In fact, the author of the epic poem "Beowolf" was anonymous. Project Gutenberg, the site for works in the public domain, has a list of writings authored by "anon" or "anonymous."