Wrong size and configuration.
Another big clue is their proliferation onto the internet.
There are more smaller sign fakes than smaller sign originals being offered all over the internet, in stores, flea markets, swap meets, etc.
In my years selling advertising it has been clear that Coca Cola was perhaps the most prolific in brand representation because they were in so many locations. Once you get into transportation related signage the locations that would have utilized original signage become a much smaller market share. International and White signage in comparison to Coca Cola would be minuscule. Yet a quick google image search turns up a number of these signs within the last 12 months compared to the previous decade.