Posting this for future reference.
After purchasing my Mack bulldog sign, I searched up & down (and even called a couple members) looking for pictures of an original. The only threads found here on OldGas, were ones with pictures that were hosted by other websites & were no longer viewable. So I wanted to post this so that anyone else searching in the future can be sure what they have.
I have been told there are very accurate repops out there... I have posted a picture below of the most common & obvious repop with a plain white back, but I am also told that there is a better repop version that has a cream colored back with old-style hangers & rack marks too. I could not find a picture of one so if someone has a picture, please post as it would be very helpful to others in the future. I know other OldGas users might be able to provide a little more info on this subject as well.
The real versions all have GREEN backs, and are all single sided with hangers on the back like the one posted below. These signs were used to hang on the top of the oval Mack pole signs, which a complete one (below) can be seen on Ebay (400550858497).