A lighting subsystem and a light bar structure upon which the lighting subsystem is mounted. The lighting subsystem has a display that incorporates both warning signal lights and a programmable message display and is configured to enable the positioning of the lighting subsystem in multiple positions, including a low-profile position and a higher profile position. In one embodiment, the lighting subsystem utilizes an LED matrix display which includes interleaved message-display LEDs and warning-signal LEDs. The system may be positioned at an aerodynamic pursuit angle, and the LEDs may be oriented to maximize forward intensity of the emitted light in the pursuit position. In the low-profile position, the lighting subsystem may be retracted into a recessed compartment in the roof of an emergency vehicle. The message display may be configured to display preprogrammed messages or user-programmed messages, and may be operable by a user outside the vehicle using a remote control.