At the time, everyone with a Manhattan mailing address seem to fancy himself or herself some sort of artist.
If not a dancer or an actor or a painter, then an artist at making omlettes, or a pick-up artist. No study or discipline was required: these were the days of the punk ethos, learn by doing.
So the streets of Soho and East Village were full of homemade posters, band posters, political posters, and just-for-the-art-of-it posters.
In those days just before home computers became popular, a great deal of street art was based around another recent technological marvel, the photocopier.
"Xerox Art", the clipping and pasting bits of magazines into angry and ironic collages, was big among rebellious teens of minimal talent, like me.