I don't know if you used the search box to look for older posts on telling the originals from repros on the Standard signs, but I had posted on one of those threads the easiest way I know to check.
The corners on the repros are sharper than originals, so I told about the "half dollar test". The curve of an original sign corner follows the curve of a US half dollar coin exactly. On a repro it will not, it's too sharp. I had posted photos in that thread as well, but I'm not sure with the age of the thread if it will still show the photos.

Darin Sheffer
Always looking for Mobil items I don't already have!