In the context of cognitive radio, this paper addresses the challenge of OFDM system identification. We show that it is possible to take advantage of pilot tone structures to perform identification. Pilot subcarriers usage is of great interest since it enables to discriminate OFDM systems that have the same modulation parameters (subcarrier spacing, cyclic prefix duration, etc.). The proposed method relies on the periodic redundancy often induced between pilot symbols. We demonstrate that most OFDM systems (Wifi, WiMAX, DVB-T, etc.) can be identified thanks to this redundancy by conducting a hypothesis test based on second order statistics. Detailed numerical examples demonstrate the efficiency of the proposed identification criterion in various kinds of environments.