from Wikipedia: Penny-loafers
The Norwegians producing leisure slippers of the moccasin style in the 1930s began exporting these to the rest of Europe where they were taken up by visiting Americans, and championed by the American Esquire
magazine. The Spaulding family in New Hampshire started making shoes based on this design in the early 1930s, naming them loafers
, the general term for slip-on shoes that remains still in use in America. In 1934, G.H. Bass (a bootmaker in Wilton, Maine) started making loafers under the name Weejuns
(sounding like Norwegians). The distinctive addition was a strip of leather across the saddle with a diamond cut-out. Initially only worn in the summer at home, the shoe grew in popularity in America to become a significant part of men's casual shoe wardrobe, though back in Europe its ubiquity has never reached the same degree. When American prep. school students in the 1950s wishing to make a fashion statement took to inserting a penny into the diamond-shaped slit on their Weejuns, the name penny loafer
came to be applied to this style of slip-on and has since stuck, though the practice itself does not continue.