Certainly in the UK and ETO in general, after 'VE' Day, 'Buzz' numbers or, in the RAF, Serial Numbers, were applied to wing undersides, in order to identify (unauthorised) low-flying aircraft.
What had been a 'Service necessity' on operations, was now considered a nuisance by the civilian population and, after numerous complaints, the 'Authorities' decided to regulate such actions, and 'charged' individuals found guilty of low-flying, when identified by the 'Buzz'/Serial numbers, newly applied.
Some possibly 'got away with it' by flying inverted ................. boys will be boys !!!