  The hidden Stueckelberg Z' model is augmented by a pair of Dirac fermions. If
the Z' has a coupling strength comparable to weak scale coupling, one can show
that this hidden fermion-antifermion pair could be a milli-charged dark matter
candidate with a viable relic density. Monochromatic photon flux coming from
the Galactic center due to pair annihilation of these milli-charged particles
is calculated and is shown to be within reach of the next generation gamma-ray
experiments. Characteristic collider signature of this theoretical endeavor is
that the Stueckelberg Z' boson has a large invisible width decaying into the
hidden fermion-antifermion pair if kinematically allowed. Singly production of
this Z' boson at the LHC and ILC are studied.
