The RN stands for Robinson Nugent, the company that made the plastic carrier. Stock chips have a silver label on the top that you can read between the ribs on the carrier, and will say Delco and something like AXCA or CMX or BBKJ and some numbers. Aftermarket chips usually have a sticker in the same place to cover the window and a second sticker on the bottom so you can read the details when the chip is out of the ecm. If it doesn't have the Delco label, it's aftermarket, and if it doesn't have any other markings the only way to begin to tell what it is is to read it with a chip programmer and start looking at the data.
