  We discuss effects of surface perturbations on equilibrium surface currents
which contribute to orbital magnetization and orbital angular momentum in
systems without time reversal symmetry. We show that, in a U(1) particle number
conserving system, disorder and other perturbations at a surface do not affect
the equilibrium surface current and corresponding orbital magnetization due to
a sum rule which is analogous to Luttinger's theorem. On the other hand, for a
superfluid, the sum rule is no longer applicable and hence the surface mass
current and corresponding orbital angular momentum can depend on details of a
surface.
