The same way one would identify them for any product. From cars to smartphones. Aftermarket things are wonderful in some cases and work just fine. However that isn't always the case. Take automobile windows (windshields, back glass, door glass, quarter glass, etc.). Some aftermarket glass, even though may actually be made through the same company that makes the OEM version (which also happens with a lot of products), they can also be of a lower quality, have different options/colors/features, etc. Even a 'slight' difference in glass thickness can make a world of difference in how well it holds up. As I have said before, not all aftermarket stuff is 'bad', but some things are worth the cost.