I found a Good Gulf plate as well that has the (R) copyright symbol next to the Gulf and my book shows it without. This does not have the (R) at the bottom right like most of the other ones I've seen. Is this a good one?
I had seen that Good Gulf image you linked Keystone and had searched the site for others. The repop looks flat, it has a white outer border and the orange is thicker. The "F" is different too in those pictures. The one I found has the curve and border looks right but the (R) marks are different. The "F" matches as well.
Would the (R) marks vary from sign to sign or maybe year to year?