I think it might well be one of a batch of Repro's that were being sold by a dealer at Kempton & Peterboro. He always seems to have a different " very Rare " Bicycle or motor dealership enamel every time he stalls. Definitely had a " good " repro of these which a well known bottle dealer bought by mistake at Kempton. Basically they are very clever made to deceive fakes. Unfortunately the real BIG money in transportation signs seems to be drawing in the fraudsters.
Some of these signs are VERY , VERY plausible...............for whats its worth my advice is IF you have any doubt at all LEAVE well alone !!
Just found 2 others sold in last few years, both have fixing holes nearer the top between W & D and above the other D in Hudson ..........so who knows !