Ummmm....call me oldschool....but isn't the fact that it is a Mustang indicitive of it being powered by Ford??? Although it is not all that big, the concept kinda reminds me of the Civic guys that have a big banner that says "Powered by Honda"...to which I generally reply "Ah, no $hit", or "No, I think it is powered by gasoline"....
If something similar wasn't used on the Shelby GT I don't think anybody would care about these things.
On the other hands some badges which are exactly the same as the ones used on the Shelby GT are going for more than $180 a set on ebay now. See here