"Happy 16th Birthday - Walt Disney World" pin-back button. Features an illustration of a dancing Snow White and the Seven Dwarfs. Diameter: 2.25". Dates from 1987. Worn by cast members to mark the 16th year of operation for the theme park. Artwork was designed by Disney artist Don "Ducky" Williams.
Special thanks to François Monferran and FrenchDisneyFan for supplying additional information for this post.