Recent theoretical predictions of anisotropy-induced polarization components in the signal wave generated from gas-phase degenerate four-wave mixing spectroscopy are verified experimentally by probing optically pumped ensembles of jet-cooled molecules that are characterized by well-defined orientation and/or alignment parameters. Aside from corroborating recent multipole moment analyses, detailed simulation of recorded data sets demonstrates the feasibility of performing a new class of resonant four-wave mixing measurements designed to extract angular momentum anisotropy information from target species in a manner that is both background-free and insensitive to isotropic contributions.