In Nottingham, as many other places all over the world, the phrase and the distinctive accompanying doodle—a bald-headed man (possibly with a few hairs) with a prominent phallic nose peeking over a wall with the fingers of each hand clutching the wall, was to be found in public WC's, walls, lamp-posts... all over the place.
I found the source site that might be of interest about 'Kilroy was here'. Here is an extract of part of it:
Kilroy and Hitler - The Rumour
Near the end of World War II, Adolf Hitler was absolutely and completely paranoid regarding one insurgent in particular. This individual seemed able to get into everything and anything that was thought to be secure in Nazi, Germany. He (Hitler) ordered his best men to begin actively searching for this super-spy and all troops were commanded to shoot and kill this menace.
The 'spy' Hitler was looking for was none other than Kilroy! GIs in occupied territory and spies in the German Army were vandalizing Nazi bases and equipment with the Kilroy logo and its well-known slogan. It wasn't intended as anything more than graffiti and a prank, but by the final year of Hitler's reign, he was convinced Kilroy could penetrate into any secure area and feared for his own safety thinking Kilroy was certain to kill him.
Origins:
Oddly enough, as widespread as the Kilroy phenomenon was there is no concrete evidence to verify either when or where it began, nor who began it in each country (USA, England and Canada). In England, the Kilroy logo was known as Chad and his slogan consisted of 'Wot no...?' The blank was usually filled in with whatever there was a shortage of or whatever was being rationed at the time. The Oxford English Dictionary states that Chad's origin is obscure, but that British Cartoonist George Edward Chatterton may have created it. Though the James J Kilroy story seems to be the most likely point of origin for the 'Kilroy was here' legend, there is possible evidence of occurrences of the Kilroy logo much earlier than World War II.
Though Chad was popular in England, just as Kilroy was in the US military, still nobody (other than James J Kilroy) has stepped forward to claim him as their own invention, even though there were 26 men named Kilroy in the military during WW2. There was also a Canadian version known as Clem and in the late 1960s there was a version in Los Angeles, California that went by the name of Overby. Perhaps the theory of Kilroy being an unknown super soldier wasn't so far off after all...?