This paper proposes a novel radar based approach for chipless tag discrimination. The proposed technique can be considered as a first step towards chipless authentication of manufactured products. The concept of chipless radiofrequency identification (RFID) is extended to tag discrimination, where each tag produces a unique signature that is very difficult to reproduce even if a clone of the device is made. The proposed technique, using radiofrequency (RF) electromagnetic (EM), keeps non-invasive and non-destructive. This new method to discriminate tag's RF signature is introduced based on the comparison between two resemblance metrics in the frequency domain and time domain. To calculate the resemblance between different signatures entire part of the RF signatures is exploited to utilize the maximum signals' richness. Owing to the chipless RF approach, we show that geometrical variations less than 10 µm (i.e., smaller than λ/1000) can be detected which demonstrate the extreme sensitivity of the method.