  We report the discovery of a strong emission line near 24.8 angstrom (0.5
keV) in the newly discovered X-ray binary system MAXI J0556-332 with the
reflection grating spectrometer onboard the XMM-Newton observatory. The X-ray
light curve morphology during these observations is complex and shows
occasional dipping behavior. Here we present time- and rate-selected spectra
from the RGS and show that this strong emission line is unambiguously present
in all the XMM observations. The measured line center is consistent with the
Ly-alpha transition of N VII in the rest frame. While the spectra contain
imprints of absorption lines and edges, there appear to be no other
significantly prominent narrow line due to the source itself, thus making the
identification of the 24.8 angstrom line uncertain. We discuss possible
physical scenarios, including a gravitationally redshifted O VIII Ly-alpha line
originating at the surface of a neutron star or an unusual donor with an
extremely high N/O abundance (>57) relative to solar, that may have produced
this comparatively strong emission line.
