According to Wikipedia about Keith Haring:
Haring achieved his first public attention with chalk drawings in the subways of New York. These were his first recognized pieces of pop art. The exhibitions were filmed by the photographer Tseng Kwong Chi. Around this time, “The Radiant Baby” became his symbol. His bold lines, vivid colors, and active figures carry strong messages of life and unity. Starting in 1980, he organized exhibitions in Club 57. He participated in the Times Square Exhibition and drew, for the first time, animals and human faces. In 1981 he sketched his first chalk drawings on black paper and painted plastic, metal and found objects.