In this paper, a detailed study is proposed on the properties of UHF RF identification (RFID) signals when the communication between the reader and tag is established. The main objective is to analyze the harmonics produced by the chip and radiated by the tag antenna. From experimentation, the characteristics of the nonlinearities contained in the signals are highlighted and linked to the theory of the backscattering in the RFID context. Several experiences taking into account the standards are proposed. Moreover, several commercial tags are considered in order to compare the observations. The used configuration, the experimental setup, and the protocols are described in detail. In particular, the generation of periodic and reproducible sequences of bits is introduced and its advantages are emphasized. Finally, contrarily to the classic approaches that tend to eliminate the harmonics generated by the rectifiers of tags, the great interest of the possible exploitation of backscattered harmonics is discussed in perspectives and some ideas of applications are given.