http://en.wikipedia.org/wiki/Kilroy_was_here wrote:
<<Kilroy was here is an American popular culture expression, often seen in graffiti. Its origins are debated, but the phrase and the distinctive accompanying doodle—a bald-headed man (possibly with a few hairs) with a prominent nose peeking over a wall with the fingers of each hand clutching the wall—is widely known among U.S. residents who lived during World War II.
The figure was initially known in Britain as "Mr Chad". Chad would appear with the slogan "Wot, no sugar", or a similar phrase bemoaning shortages and rationing. He often appeared with a single curling hair that resembled a question mark and with crosses in his eyes. The phrase "Wot, no —?" pre-dates "Chad" and was widely used separately from the doodle. Chad was used by the RAF and civilians; in the army Chad was known as Private Snoops, and in the Navy he was called The Watcher. Life Magazine in 1946 said that the RAF and Army were competing for claiming him as their own invention, but they agreed that he had first appeared around 1944. The character resembles
Alice the Goon, a character in Popeye who first appeared in 1933; another name for Chad was "The Goon".
"Foo was here" graffiti is said to have been widely used by Australians during World War I: "He was chalked on the side of railway carriages, appeared in probably every camp that the 1st AIF World War I served in and generally made his presence felt." If this is the case, then "Foo was here" pre-dates "Kilroy was here" by about twenty years. The phrase "Foo was here" was used from 1941–45 as the Australian equivalent of "Kilroy was here". "Foo" was thought of as a gremlin by the Royal Australian Air Force during World War II, and the name may have derived from the 1930s cartoon
Smokey Stover, in which the character used the word "foo" for anything he could not remember the name of.
The phrase may have originated through United States servicemen, who would draw the doodle and the text "Kilroy was here" on the walls and other places they were stationed, encamped, or visited. Brewer's Dictionary of Phrase and Fable notes that it was particularly associated with the Air Transport Command, at least when observed in the United Kingdom.
In the 1948 Looney Tunes cartoon Haredevil Hare, whilst commenting on being the first one to walk on the surface of the moon Bugs Bunny is seen walking right past a large slab of moon rock etched with the words "Kilroy was here".
Isaac Asimov's 1955 short story The Message depicts a time-travelling George Kilroy from the thirtieth century as the writer of the graffiti.
An early example of the phrase being used may date from 1937, before World War II. A US History Channel video broadcast in 2007, Fort Knox: Secrets Revealed, includes a shot of a chalked "KILROY WAS HERE" dated 5/13/1937: Fort Knox's vault was loaded in 1937 and inaccessible until the 1970s, when an audit was carried out and the footage was shot.
According to one story, it was reported that German intelligence found the phrase on captured American equipment. This began leading Hitler to believe that Kilroy could be the name or codename of a high-level Allied spy. At the time of the Potsdam Conference in 1945, it was rumored that Stalin found "Kilroy was here" written in the VIP's bathroom, prompting him to ask his aides who Kilroy was. War photographer Robert Capa noted a use of the phrase at Bastogne in December 1944: "On the black, charred walls of an abandoned barn, scrawled in white chalk, was the legend of McAuliffe's GIs: KILROY WAS STUCK HERE.">>