I always pay attention to the vehicle and how it's equipped, not the asshole inside of it.
I saw an plain tan wrapper at work the other day, parked in the firezone. Normal plates. I really wanted to call it in and get someone riled up. Lights gave it away. Anyways my bro is a squad car cop in milwaukee, he will either run/jog to work or drive his truck. The cars are out almost 24/7 with 3 shifts run through them.
BTW if it has a 'puter in the passenger seat, it's probably a cop (detective) too. I learned that the hard way.