In principle, inflation generates both scalar and tensor anisotropies. If we assume that the two spectra come from a single underlying inflationary potential their amplitudes and slopes are not independent. This leads to an algebraic consistency relation between the ratio of the tensor and scalar perturbation spectra and the tensor spectral index. However information on the tensor contribution to the spectrum is limited by cosmic variance and is easily confused with other effects such as those of a cosmological constant or tilt of the initial spectrum. In principle, this extra information may also allow one to reconstruct the low order derivatives of the inflaton potential.
Similar considerations apply to causal generation of fluctuations without inflation.
All cosmological defect models bear aspects of the latter class. The hallmark of an active generation mechanism is the presence of vector modes. Vector modes decay with the expansion so in a passive model they would no longer be present by recombination. Polarization is useful since it provides a unique signature of vector modes in the dominance of the B -mode polarization.