If you want to be as safe as possible (meaning: seen) then go with a light bar. However, I believe POV's should stick with interior lights with clear lenses in hidden spots or have a bar with colored lenses (reason being it keeps the driver safer due to a lesser chance of being thought of as a cops and keeps them from being accused of being an impostor).
One thing to note about a slick top, esp a POV without markings, is you will need more lights and more patience then a marked car with a roof bar. My county has 2 black CVPI traffic cars that were bought at the same time and outfitted with the same set up. Both had PAR36 leds in the grill, wig-wags, led mirror beams, a full inner edge (older model with the brighter liberty style heads) front and rear, separate traffic adviser, strobes in the front corners and all 4 tail lamps, and 2 TIR3's in each of the rear side windows. Due to a state law issue, one of the cars ended up getting a full liberty added to it also. After speaking with both the driver's (one of whom is a good friend of mine) and seeing them both in action, the one with the light bar is seen easier, though the slick top is still super bright. All of that to say this: even with the best slick top set up, a bar, even a mini bar, is better.