APA (7th ed.) Citation

Great Britain. Sovereign (1760-1820 : George III) & George III, K. o. G. B. By the King, a proclamation: Declaring the cessation of arms, as well by sea as land, agreed upon between His Majesty, the most Christian King, and the Catholic King, and enjoining the observance therof.

Chicago Style (17th ed.) Citation

Great Britain. Sovereign (1760-1820 : George III) and King of Great Britain George III. By the King, a Proclamation: Declaring the Cessation of Arms, as Well by Sea as Land, Agreed upon Between His Majesty, the Most Christian King, and the Catholic King, and Enjoining the Observance Therof.

MLA (9th ed.) Citation

Great Britain. Sovereign (1760-1820 : George III) and King of Great Britain George III. By the King, a Proclamation: Declaring the Cessation of Arms, as Well by Sea as Land, Agreed upon Between His Majesty, the Most Christian King, and the Catholic King, and Enjoining the Observance Therof.

Warning: These citations may not always be 100% accurate.