My grandpas Octagon Dunlop Tires sign

This ol 1920s Double sided Porcelain Octagon Dunlop sign was found in my Grandfathers garage when i was 7 yrs old shortly after he passed away. I'm 40 now and still have it hanging on my wall. I did some research on it lately consulting with museums and collectors from across Canada to the UK and found it to be a special order from the 20s and cant find another like it. its a Double Sided 2' x 2' Porcelain Octagon Hanger. its past owner my Grandpa was a RCAF Vet with the 422nd in WWII. I touched it up a bit with some easily removable black paint but left one side original (pic3). Thanks for your interest and happy hunting