On July 3, 1940, DC Comics hosted “Superman Day” at the New York World Fair.  This featured the first public appearance of Superman in costume at the World of Tomorrow:

You can see that “Superman” is spelled out over the S on his chest.  Old school!

There was a radio broadcast of Superman performed live at the Fairground, and several athletic contests for super-kids to participate in. Here’s a signup form for the events:

The event was a stunt to support DC’s World Fair Comics, available exclusively at the Fairground.

Fun stuff.  Here’s some footage from the day, including some of the athletic events!