An image of the Qawasim flag as depicted in the 1820 General Maritime Treaty between British Empire and Al Qawasim. A figure of the flag can be seen on page 113 of Coll 30/15 'Anthems and Flags of Various States. Bahrein [Bahrain], Koweit [Kuwait], Muscat, Asir, Yemen, Qatar, Trucial, Oman' [‎57r] (113/261) created in 26 Jun 1917-7 Apr 1941 and published in the British Library: India Office Records and Private Papers. 
This image is of my creation copying the original Qawasim flag as drawn in the treaty. As the original flag was hand drawn in the treaty and no modern image of the flag is available as the flag use has been discontinued, it is impossible to accurately determine if the colors, diameter, and Arabic calligraphy is 100% accurate to the flag that has been flown by the Qawasim prior to 1820.

This is the original flag of Al Qawasim according to Sheikh Sultan bin Muhammad Al Qassimi, the Ruler of Sharjah. The Arabic calligraphy reads "A victory from Allah and an imminent conquest".[1]
Own work, created from Coll 30/15 'Anthems and Flags of Various States. Bahrein, Koweit, Muscat, Asir, Yemen, Qatar, Trucial, Oman' ‎57r (113/261)
Limghadar