At risk of exposing my rather shallow knowledge of the topic, one aspect of PoMo is "everything is an inauthentic quote of something else and everything has already been done to death - so embrace irony and self-reference and achieve sincerety by self-awareness of your own insincerity".

This sounds like pop art—which some see as a precursor to post-modern art, and some see as an early type of post-modern art.