In the late 1960's, the T-shirt became a means of self expression as wearable art as well as to convey commercial advertising, souvenir messages, and protests. Psychedelic artist Warren Dayton pioneered several political, and pop-culture art T-shirts featuring images of Cesar Chavez, political cartoons, and other cultural icons of that era. The designs produced in the 1970's are just as popular today as they were then, if not perhaps more so. Some of the more notable shirt designs over the decades include the yellow happy face T-shirts,