The aim of this work is to show that the emitted signals of a double-output laser cavity exhibit distinctive features, manifesting themselves through typical dissymmetry in the corresponding spectral line shapes. Usually, such a dissymmetry in an inhomogeneously broadened gas laser appears with a clear but unpredictable shift of the maximum intensity level either towards the high or towards the low frequency sides with respect to line centre. In the case of a double-output laser, the spectral profiles show opposite shifts. This means that when the maximum intensity of one output moves towards the high frequency side of the profile, the maximum intensity of the other moves towards the low frequency side. This gives rise to a frequency shift, with respect to the Lamb-dip for a classical laser On the theoretical side, we apply the standard disturbed Gaussian beam model to give a good quantification of the frequency shifts obtained at both sides of the system.