 Abigail Goldman of the Los Angeles Times , wrote that the smiley face and the expression " have a nice day " " helped to define the ' 70s " . In the early 1970s , Philadelphian brothers Murray and Bernard Spain designed and sold products including bumper stickers and coffee mugs that each contained the yellow smiley face , usually attributed to Harvey Ball . They later changed the phrase to " Have a nice day " . 
