1939 - The Crystal Ball Girl Scout Bar Pin was first offered in the Girl Scout catalog in the fall. A memento for the 1939 World's Fair, it came with an image of the Girl Scout Chalet - the newly opened Girl Scout/Girl Guide center in Switzerland. To honor this, the Girl Scouts built a smaller replica at the World's Fair in New York that worked as an information center and focal point for Girl Scouting. 

The "crystal ball" was held together by a metal band with the trefoil
on it. If the band was unscrewed the ball separated into two pieces,
allowing the owner to insert a new two-sided picture in place of 
the trefoil and Chalet.

More commonly seen is the necklace version of this item.