The explanation I heard was that during the second world war, as the US and British forces advanced in Europe, the Americans would chalk 'Kilroy was here' on so

The explanation I heard was that during the second world war, as the US and British forces advanced in Europe, the Americans would chalk 'Kilroy was here' on some landmark, and the British would add the Chad graphic, reminiscent of a gang sign. 'Chad' used to be associated with protests against shortages due to war rationing, a forlorn figure peering over a wall exclaiming "Wot, no fish?" or "Wot, no sugar?"