There was no agreed upon a League of Nations flag. One possible variant is shown here:
During its entire existence the League of Nations could not agree on one single symbol, although in the year of its foundation, 1920, there were proposals for it. This was a blue flag, which had in a white design an oval world map, enclosed by a elliptic ring consisting of as many stars as there were member states. The League of Nations organisations used it for their own operations, but there was no success in having the League of Nations itself to adopt it. Where it was active, like in Danzig or Saarland one used improvised emblems or none at all. In 1929 there was an international contest for a design. On 1 January 1930 there were 1640 proposals, out of which an international jury chose 50. Finally it was decided that none deserved first prize: two second prizes were awarded and three third prizes. The fear that a supranational organisation might become more powerful than the member states lay at the bottom of this hullabulloo. In 1939, as the political role of the League of nations was nearly nil a semi-official emblem emerged: two five-pointed stars within a blue pentagon. A white flag with this emblem was hoisted on top of the pavillion of the New York World Exposition and flew there during two years. The pentagon and the five-pointed stars were supposed to symbolize the five continents and the 'five races' of mankind. In a bow on top and at the bottom the flag got the names in English and French for the League of Nations.