In complex systems, the assignment of IR and VCD bands associated to the excitation of particular vibrational modes in a molecule, which can be interpreted as the vibrational signature of that molecule, often turns out to be a cumbersome task . This is due, for instance, to anharmonic effects arising at increasing temperature, or to the presence of an environment, e.g., a solvent, that can mask the vibrational signature of the solute molecule of interest. In addition, while molecular dynamics (MD) simulations at finite temperature are able to realistically capture those effects in IR and VCD spectra, applying a standard normal modes analysis for their interpretation is clearly not sufficient, since a theory beyond the harmonic approximation is needed.