If you're legally allowed, which was noted above, here's what I'd do.
For the rear, install simple LED deck lights. I don't recommend any one brand, because they go on sale all around the internet at different times, and I don't wanna say get a Feniex, when you can get an equally good Whelen (for example) for cheaper. Browse around, and find some deck lights, my personal choice was a feniex cobra 100. I placed this on my rear deck in the middle, so when it's not on, it just looks like a rear window brake light.
When you're looking at the sides of the vehicle, one thing I think would work extremely well with your vehicle would be these little lights I've been seeing all around now.
http://www.sirennet.com/wh0s-0--cr.html Although those are chrome and not the brightest, I have seen many with black finish, or none at all, and are very bright. They can be placed around your vehicle very easily, they won't attract any real attention, and you'll get the job done very easily.
When it comes to the front, you will obviously want some sort of light there, but what kind is really up for debate. My personal setup includes a little dash light that's wired in such a way that when I'm not using it, I just pop it in my glove box. That way, when it's parked on the side of the road, people don't see anything that makes it look like anything more than a regular car. The biggest reason I went with a suction mount dash light was because our team does evidence searches a lot, and when you're looking around for evidence at a crime scene, and you're parked somewhere where you can't see your car, you don't really want anything saying "Hey, I'm working with the police here. Feel free to beat up my car" because unlike the police officers, if my car gets beat up, I can't just get a new one from the lot.
Hide-a-ways have been something I've seen around a lot too, little LED or strobe lights in the head and tail lights. I don't have them personally, and I've never installed them, so I don't know what it's like labor wise, but they do make for a very discreet place to be very visible.
One last thought is an overhead light of sorts. Here we don't have any laws regulating lights except flashing reds. Blue I find to be the most visible light, and for this reason, I picked up a little locally made LED minibar for my car. It's magnet mount and cig-light run, and all blue. I've only ever used it once for a scene, but it was terrible weather, and I put it on top of my car because the snow kept piling up on my rear window faster than the heater could melt it, effectively rendering my interior light useless. I don't know how it'd hold up as a permanent light, nor do I really wanna test it, but it has served well as a beacon when the weather sucks, so perhaps looking into even something such as a cig-lighter beacon would be in your best interest.
Just make sure to check with local laws before doing it. Here they don't have really any restrictions, but I've heard of some places where you can't even run amber lights without getting permission from the state to do so
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