A vehicular exterior rearview mirror system includes an exterior rearview mirror assembly having a mirror casing portion and a mirror reflective element sub-assembly having a mirror reflective element. The mirror reflective element sub-assembly includes a mirror back plate. A heater pad is disposed between a side of the mirror back plate and the mirror reflective element. The mirror reflective element is fixedly attached to the mirror back plate with the heater pad disposed therebetween. The mirror reflective element sub-assembly includes a display indicator having a light source that is activatable to emit light. When activated, the light source emits light that transmits through a light-transmitting passageway of the display indicator and through a light-transmitting portion of the heater pad and through the mirror reflective element to be viewable by the driver of the vehicle. The display indicator is associated with a blind spot detection system of the vehicle.