To qualify as a memristor, the pinched hysteresis loop of a dynamical system corresponding to a sinusoidal excitation signal must be pinched at the origin, for any amplitude, and for any frequency, as well as for any initial condition of the state variable. The above conditions can be checked by the simulations which should be repeated as many times as possible. However, the times of simulation are limited, the finite results drawn through the simulation are not necessarily reliable. To increase the reliability of the judgment, a generalised mathematical model of memristor is designed in the study, which confirms three fingerprints of memristor. HP memristor, piecewise-linear memristor, memristor with square non-linearity and memristor with cubic non-linearity are included as generalised memristor model special cases. The generalised mathematical model of memristor is applied to distinguish memristor from three mathematical model examples. A generalised mathematical model of memristor is a necessary, but not a sufficient condition for judging whether the dynamical system is or not a memristor, which may save us a lot of time and energy.