159,524
Puts on captain's hat...
"Kilroy was here" was a memetic practice done by the US army, during the second world war, that involved US soldiers scribbling the figure wich I posted, everywhere they went, along with the line "Kilroy was here".
The figure was commonly found to comfort US soldiers, whenever they saw it, because, where ever they were, if they saw Kilroy, it meant that someone has been there before them.
I suppose "Foo was here", is just the Australian equivalent...