  We present a posteriori error analysis in the supremum norm for the symmetric
interior penalty discontinuous Galerkin method for the elliptic obstacle
problem. We construct discrete barrier functions based on appropriate
corrections of the conforming part of the solution that is obtained via a
constrained averaging operator. The corrector function accounts properly for
the non-conformity of the approximation and it is estimated by direct use of
the Green's function of the unconstrained elliptic problem. The use of the
continuous maximum principle guarantees the validity of the analysis without
mesh restrictions but shape regularity. The proposed residual type estimators
are shown to be reliable and efficient. Numerical results in two dimensions are
included to verify the theory and validate the performance of the error
estimator.
