The unofficial flag shows a blue ground. It stands for the ocean and the yellow half-disc for the sun. In the center of the flag is placed a stylized depiction of the main-island Chatham. The flag is unofficial, what means that there is no official approval or legal regulation that states that this flag is to be recognized as a symbol of the island. It comes from a private initiative and is only used by private individuals. Officially, the flag of New Zealand has to fly here.
When the British seafarer William Robert Broughton discovered the island on 29th of November in 1791, he named it after his ship the "HMS Chatham". This was named after John Pitt, 2nd Earl of Chatham, First Lord of the Admiralty.