Observational distinction between black holes and naked singularities:   the role of the redshift function
  We suggest that the redshift of photons traveling from past to future null infinity through a collapsing object could provide an observational signature capable of differentiating between the formation of a globally naked singularity and the formation of an event horizon. Supporting evidence for this idea is drawn from the analysis of photons with zero angular momentum through the center of a collapsing spherical dust cloud. We show that the frequency shift as a function of proper time with respect to stationary observers has distinct features depending on whether the object collapses to a black hole or a naked singularity. 
N\'estor Ortiz, Olivier Sarbach, and Thomas Zannias
gr-qc astro-ph.CO