The WWII generation is getting smaller, but they will know about the phrase "Kilroy was here" which was well known during and after WWII. But for younger readers, the phrase and its origin might be unknown.
Its origins are debated, but the phrase and the distinctive accompanying doodle of a bald-headed man (sometimes depicted as having a few hairs) with a prominent nose peeking over a wall with the fingers of each hand clutching the wall — became associated with American soldiers during World War II.
It became what we would term today a "meme" though that term didn't appear until 1976.
The legend was that "Kilroy" was a shipyard worker during the war who worked as a checker at the Fore River Shipyard in Quincy. His job was to go around and check on the number of rivets completed. He would count a block of rivets and put a check mark in semi-waxed lumber chalk, so the rivets wouldn't be counted twice. When Kilroy went off duty, the riveters would erase the mark.
To keep things more honest, he started to put his check mark on each job he inspected, but added 'KILROY WAS HERE' in king-sized letters next to the check, and eventually also added the sketch of the face with the long nose peering over the fence and that became part of the Kilroy message.
Kilroy's inspection "trademark" was seen by thousands of servicemen who boarded the troopships the shipyard produced. It connected with servicemen and they picked it up and spread it all over Europe and the South Pacific.
Before the war's end, "Kilroy" had been everywhere from Fort Dix, New Jersey, to Berlin and Tokyo. It was somewhat mysterious but clear that Kilroy had "been there first."
At the war's end, in 1945, an outhouse was built for the exclusive use of Franklin Roosevelt, Stalin, and Churchill at the Potsdam conference. The first user was Stalin, who emerged and asked his aide (in Russian), "Who is Kilroy?"
In 1946 the American Transit Association, through its radio program, "Speak to America ," sponsored a nationwide contest to find the real Kilroy, offering a prize of a real trolley car to the person who could prove himself to be the genuine article.
Almost 40 men stepped forward to make that claim, but only James Kilroy from Halifax , Massachusetts had evidence of his identity. To help prove his authenticity, 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 yard in Halifax , Massachusetts.
In the United Kingdom, the graffiti is known as "Mr Chad" or just "Chad", and the Australian equivalent to the phrase is "Foo was here".
In the 1950s, even non-soldiers took up the phrase and added the graffiti logo in unlikely places. Legend has it that it appears atop Mt. Everest, on the Statue of Liberty, the underside of the Arc de Triomphe and that it is scrawled in the dust on the moon.
It was engraved into the WWII Memorial in Washington, DC.