Foo was here

"Foo was here" is an Australian graffiti signature of popular culture, especially known for its use during World War II, but also became popular amongst Australian schoolchildren of post-war generations.

Foo (or Mr Chad) is shown as a bald headed man (sometimes depicted with a few hairs) peering over a wall (usually with three fingers from each hand appearing to clutch over the wall as well), with the simple inscription "Foo was here".

While its exact origins are unknown, the "Foo was here" graffiti is said to have been widely used by Australians during World War I and also during World War II. At some point the Australian phrase combined with a popular British piece of graffiti called Mr Chad, most likely as a result of the two countries' respective armed forces working together in such close proximity.

One source says of Foo that "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" predates the American version of World War II, "Kilroy was here", by about 25 years.

It has been claimed that Foo probably came from the acronym for Forward Observation Officer, but this is likely to be a backronym.
Other sources suggest that Foo was a man that was inspecting the welds in submarines. He had to crawl inside small spaces to do this, his superiors were wondering if he was doing his job so everywhere that Foo went he would write "Foo was here". This has been found on the wreckage of many subs and ships. This trend soon caught on.

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Wikipedia