Found 2 of these in a barn in Maine. 1 was dirty and the other painted over. So after searching this site for information, and after several attempts at softer options, I started to use oven cleaner. Wow what a difference. I was afraid at first but finally saw results. I would spray and count to 6 and start vigorously wiping. The sign is painted tin. Covered the wood frame with painters tape. Came out better than expected.