I have a friend who's an artist, and he loves putting random weird things or vague symbology that doesn't particularly mean anything it his pictures. People always assume it does mean something, but since it's so vague (and he never tells them what it "means") they can never nail down exactly what it is. He's always praised as a deep and thoughtful artist because of it, and I think it's directly responsible for much of his success.
I'm not sure exactly what you mean, but the way he tells it he literally makes up random stuff that looks good and tosses it in there, so I guess his subconscious?
Basically. Unfiltered outputs from the connection machine based on environmental triggers, past memories, previously consumed culture, random hardwiring in the individual etc etc. These outputs have meaning and can be very interesting, and can have a strong and broad context embedded in them but one that is hard to pinpoint. In a word - mysterious.
People also have varyingly interesting random generators. The artist's consciousness is absolutely not necessary for art to be interesting.
