From my link
This is a reproduction of the Spanish Republican flag with the text 35 Division, 15 Brigada Internacional, size 3 feet x 5 feet, flag has both a pole sleeve and two grommets for flying from a flag pole.
In the Autumn of 1937 each of the International Brigades were presented with a flag at the Calderon Theatre in Madrid in a ceremony to celebrate the 1st anniversary of the formation of the International Briagdes.This is a depiction of that flag representing the English speaking 15th Brigade which included English, Irish, American, Canadian and Commonwealth volunteers.