Amplitude spectrum (transfer function) of signal?
HINT:
If $X(j\omega)$ is the Fourier transform of a signal $x(t)$, try to remember (or look up) how $X(j\omega)$ is related to the Fourier transform of the derivative $x'(t)$.
Some people are more familiar with this in the Laplace transform domain: the time derivative corresponds to which operation in the Laplace transform domain? Replace $s$ with $j\omega$, and you'll understand the given figure.