A warning system for a vehicle includes a vehicle door-mounted exterior illuminable signal, a door-open indicator associated with the vehicle door, and a controller configured to actuate the exterior illuminable signal to emit light in a selected one of multiple operating modes. The operating modes may include an increased visibility operating mode differing from other operating modes in an intensity and/or pattern and/or color of light emitted by the door-mounted exterior illuminable signal. The vehicle door may be a rear-hinged door and the illuminable signal may be associated with a handle of the door. The controller may actuate the exterior illuminable signal in a different operating mode on receiving both of a signal from the door-open indicator and a signal from a vehicle navigational system.