Kilroy became the U.S. super-GI who had always "already been" wherever
GIs went. It became a challenge to place the logo in the most unlikely
places imaginable (it is said to be atop Mt. Everest, the Statue of Liberty,
the underside of the Arch De Triumphe, and even scrawled in the dust on
the moon.)

 And as the war went on, the legend grew. Underwater demolition teams 
routinely sneaked ashore on Japanese-held islands in the Pacific to map 
the terrain for the coming invasions by U.S. troops (and thus, presumably, 
were the first GI' s there). On one occasion, however, they reported 
seeing enemy troops painting over the Kilroy logo! 

In 1945, an outhouse was built for the exclusive use of Roosevelt, Stalin,
and Churchill at the Potsdam conference.  The first person inside was
Stalin, who emerged and asked his aide (in Russian), "Who is Kilroy?" ...

 To help prove his authenticity in 1946, James Kilroy brought along 
officials from the shipyard and some of the riveters. He won the trolley 
car, which he gave to his nine children as a Christmas gift and set it up 
as a playhouse in the Kilroy front yard in Halifax, Massachusetts.

 The etching above is engraved on a WW2 memorial in Washington, DC

Click here for more about Kilroy and the legends that abound.