The type of cord and number of plies in the sidewall and under the tread.
Since tires play a major role in establishing the personality of a vehicle, many manufacturers require their tire suppliers to identify their Original Equipment (OE) tires with symbols or codes branded on the sidewalls.
The goal is to make it easier for owners to identify and select exact replacements when the OE tires wear out. Matching the original tires exactly helps maintain the vehicle’s integrity.
see: https://www.chevrolet.com/certified-service/tire-research