The cause and effect relationship appears to be obvious, does it not? IF you modify your vehicle, THEN you will have trouble with the the big 5-Oh (the police, that is).
That crazy paint, those shaved taillights, that sick air ride system, that bangin' stereo, that rumblin' exhaust, may be badass, but at what cost? It seems that each custom modification is accompanied by the risk of a hefty fix-it ticket or moving violation each time you roll your ride. Is this true? Probably. And get used to it, because the only way to avoid such harassment (as I sometimes consider it) is to roll completely stock. But before you get too frustrated with all that court time you're putting in and decide to have custom (and permanent) "for sale" stickers made, consider the following.
I used to live in fear of getting rolled for my custom truck. I hated the sight of cops, and thought they were all just out to get me. While some do have a "thing" against custom vehicles, I've learned that many police are reasonable. After studying Criminology for four years, here's what I've learned that might help you avoid those flashing lights behind you.
Stickers that indicate "gang" or group affiliation stand out to police. Old English across your back window, profanity, and vulgarity stand out. Personally, I roll my club's logo on the bottom of my front windshield. I've had the sticker across my back window, and was told by police to take it off if I wanted to stay out of trouble.
Primer attracts attention as well, and might give the "unsafe" and unfinished impression to police. Nitrogen bottles flopping around, exposed air ride systems, and open wheelwells scream "I'm custom, pull me over!" Cover it up!
Dark window tint is a threat to police because it means they can't see you; they can't see what you're doing, and that's not cool to them. You can see them, but they can't see you.
Your appearance matters too. Police will notice if you're sportin' the baggies and a beanie or cocked hat under a hooded sweatshirt. This isn't bad, just realize the image (whether accurate or not) might come across as threatening.
Attitude counts when you do get pulled over. The F-the-Police attitude will get you in more trouble. Throw your keys on the dash, don't get out of your car, keep your hands in sight, don't make any spaz moves, don't flip the cop off, and don't lie about anything, especially obvious modifications. Just cooperate, believe me, because you won't "win" by being a dumbass.
Don't purposely drag in front of cops, keep your ride road-worthy, and of course, don't drink and drive. Remember that cops are just people, so communicate without threatening. Keep your license, insurance, and registration up-to-date, and most of all, relax - life will go on.