Where did this all come from? Per http://en.wikipedia.org/wiki/Kilroy_was_here:
Kilroy was here is an American popular culture expression that became popular during World War II; it is typically seen in graffiti. Its origins are debated, but the phrase and the distinctive accompanying doodle — 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 GIs in the 1940s.
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. An ad in Life magazine noted that WWII-era servicemen were fond of claiming that "[w]hatever beach-head they stormed, they always found notices chalked up ahead of them, that 'Kilroy was here.'"