This armband belonged to Myer Minsky of Bangor. He wore it around 1943 as a Block Warden. Block Wardens were civilian soldiers charged with defending their towns and cities during the War. Each warden was assigned to a city block shortly after the bombing of Pearl Harbor. With their white helmets and armbands, they enforced Blackouts and Brownouts.
(If you click through to the full cataloging record on Maine Memory, you’ll see that the armband appears upside down because the image was uploaded that way. The correct presentation is as it appears here, with the peak of the triangle pointing upward.)