Would a plate/sign like the one attached below be a fake?
Yes, the one posted is a fake.
Is there a place that outlines the general specs for a real plate or sign? It would be awesome to have a resource that you can look up and tells you what sizes a real sign would be. what sizes a real sign will not be.
No. many companies used different plates & sizes. Most 11-3/4" plates are fake, and you can tell the ones on ebay most of the time by the seller's other or past items. However, there are legitamate plates that are 11-7/8"... so it has somewhat become difficult to tell for beginners.
Best advice I can give you is to buy only from a trusted source, someone that stands behind what they sell and has a good reputation in this hobby