The 'e' on the front of the pigment boxes after the weight. In the picture on the first pigment box the 'e' is how a genuine MAC pigment would be printed, it has sharp detail and fine horizontal curved lines. The last two pigments in the picture, the 'e' on the box is thick, undefined and not sharp at the edges. This is one of the signs of the slightly older fakes (the boxes are the shiny kind which mark easily), and can be seen on some of the fake eyeshadows too.