The George Rogers Clark Flag is a red and green striped banner in the model of American Flags commonly associated with George Rogers Clark, although Colonel Clark did not campaign under these colors. The “Clark” flag was made in Vincennes, Indiana, and likely flew over Fort Sackville even before Clark arrived.
On 12 November 1778, Vincennes resident François Bosseron recorded the following items under the heading ""1778 fournie au Cap Helm pour les Compagnie des États"":
This flag was designed by Captain Leonard Helm, who held Fort Sackville until forced to surrender to Lieutenant Governor Henry Hamilton. Although historians are not sure exactly what it looked like, most US flags were based on the “stripes of rebellion.” Helm’s design was clear enough that Hamilton recognized two on his approach to Vincennes, one on a boat and one on the fort. One of these may have been Bosseron's flag, although Father Pierre Gibault may have brought a flag with him. Captain Helm had earlier brought a United States flag to Ouiatenon, so it is possible that he also had brought one to Vincennes. When Hamilton took the fort, he allowed Helm to take down "the continental flag" before raising the British flag.
The choice of a red and green flag instead of red and white flag remains a mystery. It is possible that there simply was not enough white serge available in Vincennes at the time. It is worth noting, however, that whereas Colonel Clark had offered a red and white belts to American Indians in Cahokia to represent war or peace, Captain Helm presented the Wabash Indians with a red or green belts. On December 27 at Vincennes, a Piankeshaw chief presented Lt-Gov Hamilton with red and green wampum, which was said to represent the Wabash River.
The stripes, themselves, were a defining feature of British American flags even before the Revolution, and many military banners used by Americans featured stripes of differing colors. Records describe flags similar or identical to this in the 13 colonies. It is possible that Busseron ordered the banner for his own militia unit in Vincennes, when they declared for the United States.