Taken from a warning about fake Sapphires from Videogameimports.com - The orange colour (see the Arcade CD logos at the front, side and back) is a brighter shade in the counterfeit version. The original is slightly darker and is extremely lightly 'dotted' with with very tiny white dots. They are barely visible to the eye, but they are there. Looks like the counterfeiters were unable to replicate this.
The artwork on the front, of the girl, appears very slightly out of focus.
The most noticeable part is on the back cover, where there are pictures of the 2 Arcade cards. The counterfeit version is much more fuzzy looking, and the picture of the planet is unclear. With the picture of the the Arcade Card Duo, on the original version, you can see a very thin white outline around the part of the card with the artwork on it. On the counterfeit version, there is no white outline.
Suppose this only really helps if you have one to compare against, but hope this goes someway towards helping.