  We use the high-resolution HR-DEMNUni simulations to compute
cross-correlations of the Cosmic Neutrino Background C$_{\nu}$B with other
observables, namely: cold dark matter density, effective weak lensing
convergence, neutrino velocity and neutrino deflection angle. We provide, for
the first time, this high-fidelity cross-correlation maps in order to
illustrate how much can be learned from them once the cosmic neutrino
background is measured. As cross-correlations will have more signal than
auto-correlations of the C$_{\nu}$B itself, these might be the ones to be
measured first by Ptolemy-like experiments. Our predictions thus provide the
imprint of what massive neutrinos should look like from cosmological
observations.
