Ever taken a good look at the tail of a real airplane, all is in CAPITAL lettering.
Under international agreement it is not just random lettering no it tels you where the country of origin is, like N for USA, C for Canada,G for Great Britain, PH for the Netherlands, D for Germany and VH for Australia.
GA aircraft use it as Callsign as for commercial Airliners use Callsings linked to there Airlines, like British Airways are called “Speedbird” and South African Airways are called “ Springbok”.