Most famously it signals the presence of the monarch at a royal residence, and is also used on official vehicles, primarily the Bentley State Limousine, but also on other road vehicles at home or abroad, often a Range Rover.
United States | United Kingdom | Republican Party (United States) | Democratic Party (United States) | United States House of Representatives | President of the United States | United Nations | Royal Navy | United States Senate | United States Navy | United States Army | Supreme Court of the United States | United States Air Force | Native Americans in the United States | Royal Air Force | United States Congress | Parliament of the United Kingdom | 66th United States Congress | Prime Minister of the United Kingdom | 74th United States Congress | 18th United States Congress | 73rd United States Congress | 54th United States Congress | 61st United States Congress | United States Marine Corps | United States Department of Defense | 64th United States Congress | 65th United States Congress | 53rd United States Congress | 52nd United States Congress |