Observable (?) cosmological signatures of superstrings in pre-big bang models of inflation

The different couplings of the dilaton to the U(1) gauge field of heterotic and type I superstrings may leave an imprint on the relics of the very early cosmological evolution. Working in the context of the pre-big bang scenario, we discuss the possibility of discriminating between the two models through cross-correlated observations of cosmic magnetic fields and primordial gravitational-wave backgrounds.