A blind zone indicator module for a vehicular exterior rearview mirror assembly includes a hollow housing that includes a front end for attaching the indicator module at the rear of a mirror reflective element configured for use by an exterior rearview mirror assembly, a rear end opposite the front end, and an intermediate portion between the front end and the rear end. The hollow housing comprises an inner surface that is white and is diffusely reflective of light incident thereat. A diffuser element is attached at the front end of the hollow housing and closes the front end of the housing. Potting material is disposed at and over a circuit board to seal the circuit board in the module. Light emitted by a light emitting diode, when activated, reflects off the white inner surface of the hollow housing and passes through the diffuser element to exit the indicator module.