You picked a tricky one there. First of all, you’re not doing anything wrong, but ti’s not possible to put a single texture across the entire diner wall. The reason for this is the way I UV mapped it. It’s split into 3 section - left, center and right - and those sections are superimposed on the map. This means that the 3 sections share the same texture.
I did it this way for a good reason. The size of map required to cover the entire wall would be very large, or using the existing brick texture, it would render very low quality. It’s a common trick in UV mapping. Unfortunately, in this case, it means a sign texture won’t work.
The only way to do it would be to make a sign prop for the front. Check your PMs. I might be able to help you out.
Note - The Diner was never really meant to be an exterior model, which is why I didn’t add a roof, sign, etc.