We consider the minimal see-saw extension of the Standard Model with two right-handed singlet fermions $N_{1,2}$ with mass at the GeV scale, augmented by an effective dipole operator between the sterile states. We review current bounds on this effective interaction from fixed-target as well as from cosmological observations. We then highlight the prospects for testing the decay $N_2 \to N_1 \gamma$ induced by the dipole at the future facilities targeting long-lived particles FASER 2 and SHiP.