Sometimes sellers let you think a watch is a special limited edition, while it's not. Always check the picture of the G-Shock. Special editions often have a special figure in the display. Limited editions have often different color schemes than the normal ones. Limited editions cheaper models, like the DW-002 and DW-6600 are often used for advertising. The more expensive models are most of the times limited editions of special color themes like Men in Yellow, Men in Smoke, or specially designed for G-Shock by famous sportsman, artists or designers, like the 21st B.C. series, or the G-Shock's designed by Terje Hakonsen and Pinifarina.
If you are not sure if a certain model is a limited edition, try to find out the model number. If you got only the short model number, like DW-9100, just find out the regular colors. The best way is to use www.google.com and fill in the model number.
If you got the complete model number, like DW-9100BT-2T, search with google. If it is a special model, you will find it on Japanese sites with the name of the series. You will find out this example is a Terje Hakonsen Signature Riseman.
A lot of people asked me if I knew how many are made of a certain Limited Edition model. Unfortunately is the limited emission only known of the G-Shock models with a serial number or a certificate. About the other Limited Editions is only known that they are produced during a small period. Thank you FUMI, Orange 5 and Yachtrays for helping me with this topic.