“Of course, the colourful crosses, roundels and stars that adorned these early warplanes, which were actually inspired by the medieval art of heraldry, were more than just decorations. They helped pilots (and gunners on the ground) quickly separate friend from foe in the thick of combat..
https://militaryhistorynow.com/2014/05/28/flying-colours-a-vivid-history-of-warplane-insignia/