A vehicular exterior rearview mirror assembly includes a mirror reflector sub-assembly having a mirror reflective element, a mirror back plate, a heater pad, and a blind zone indication module that includes a plastic housing. When at least one light emitting diode of the blind zone indication module is electrically powered, light emitted by the light emitting diode exits the blind zone indication module via a light-transmitting portion of the front end of the plastic housing. With the blind zone indication module disposed at the mirror reflective element, and with the light-transmitting portion of the front end of the plastic housing juxtaposed with a light-transmitting aperture of the mirror back plate, light emitted by the light emitting diode passes through the mirror reflective element and illuminates an icon of the mirror reflective element that is viewable by a driver of a vehicle equipped with the mirror assembly.