In Scott Benjamin and Wayne Henderson’s book “Oil Company Signs - A Collectors Guide” , it is listed as an 18x18” flange sign. On their rarity scale of 1 to 5 , it is listed as a 4 being rare to very rare. It’s listed as being used from 1918 to 1923. It’s a cool piece of history and petroliana. As far as value I have no idea with the condition being what it is. I would put it on an old piece of weathered barn wood and keep it !
I measured it. They are saying it should be 18 inches?