I noticed a similar sign on ebay...been for sale for a long time for $2500.
As I look at the pictures of it, it looks like the back of it is ridged around the entire circumference including the feather...mine is flat with no ridge...are both ways "real"?
The ridge, or flange, is used on larger signs to attach to the metal "can" or cabinet that goes between the two sides of sign. A sign like this could have easily been part of a large outdoor porcelain neon dealer sign.