A mirror reflective element sub-assembly suitable for use for an exterior rearview mirror assembly of a vehicle includes a mirror reflective element, a mirror back plate having an indicator receiving portion established thereat, and a signal indication module having a light source. The signal indication module attaches to the indicator receiving portion of the mirror back plate and the light source is activatable to emit light through the indicator receiving portion. The light source is established at a circuit element and the signal indication module includes a housing that substantially encases the circuit element therein. The circuit element has electrical terminals extending therefrom and protruding at least partially at a connector portion of the housing so as to be electrically connectable to a power source of the vehicle. The connector portion of the housing is configured to provide a plug-socket connection between the power source and the signal indication module.