An attractive explanation for nonzero neutrino masses and small matter antimatter asymmetry of the present Universe lies in "leptogenesis". At present the size of the lepton asymmetry is precisely known, while the sign is not known yet. In this work we determine the sign of this asymmetry in the framework of two right-handed neutrino models by relating the leptogenesis phase(s) with the low energy CP violating phases appearing in the leptonic mixing matrix. It is shown that the knowledge of low energy lepton number violating rephasing invariants can indeed determine the sign of the present matter antimatter asymmetry of the Universe and hence indirectly probing the light physical neutrinos to be Majorana type. © 2006 The American Physical Society.