I would be really surprised if that sign was real. The hole pattern is wrong and the fact that it is curved throw up all kinds of red flags. I am certainly not an expert nor have I ever claimed to be, but where would that sign have been used? I have never seen a curved SHELL and if it were to be used on a visible pump, the art work would have resembled the signs during that time and in my opinion would be totally different.
Not to be obvious or anything, but your statement immediately discounts itself. "I am certainly not an expert" yet you claim the holes are in the wrong place?
I've looked at several Shell pieces this year and my initial reaction to his picture was positive. There isn't heavy shelving, the metal is thin, the style is consistent with proven originals of the same period. Whether used on a visible or other petrol related item it's hard to pinpoint. In trying to Google similar sizes I'm not running into listings for repops consistent to this one and the one's I've personally seen are typically heavier both in material and porcelain shelving. Also they tend to have yellows and reds which are brighter than originals. Compare the one from
this page. 
