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.