I do not believe that you can. There was a very limited number of SS AMX's built and they were supposely sold only to the racers that AMC sponser at the time. However I could be in error in this department. Secondly, there were some dealers (AMC) that would race these cars independently from AMC (such as Bundy AMC in Denver, Colorado). These again were limited to only a few people.
Maybe the adminsterator can tell you for sure. I do not believe that there any way as far as the vin is concern that would tell you.
Andre runs the S/S AMX Registry and can give you the details on how to identify one. While there's not a unique digit or symbol in the VIN that will tell you, the 53 cars were pulled of the line sequentially so if you have the VIN numbers that are within those 53 numbers it's an authentic S/S AMX. Andre can help you with those numbers. He may know the history of the car as well.