Nope, it isn't Forrest Gump.
In 1963 designer Harvey Ross Ball was "commissioned to create a graphic to raise morale among the employees of an insurance company after a series of difficult mergers and acquisitions. Ball finished the design in less than 10 minutes and was paid $45 for his work. The State Mutual Life Assurance Company (now Allmerica Financial Corporation) made posters, buttons, and signs adorned with the jaundiced grin in the attempt to get their employees to smile more."
I quite prefer the crudeness of Ball's smiley face over the evolved version that we see today. :)