A mirror reflective element sub-assembly suitable for use for an exterior rearview mirror assembly of a vehicle includes a mirror reflective element and a mirror back plate having a generally planar portion and an indicator receiving portion established via a plastic injection molding operation. The indicator receiving portion includes a wall structure extending at an angle from the generally planar portion adjacent to an aperture established through the mirror back plate. A signal indication module has a light source and a housing that is at least partially received at the wall structure of the indicator receiving portion of the mirror back plate. When the light source is activated, light emitted by the light source emanates through the aperture of the mirror back plate and through the mirror reflective element at an angle relative to the generally planar portion of the mirror back plate.