As I get closer to them, I start using various identifying characteristics to rule out the "unsure" vehicles. Sometimes it's very tough, requiring that I approach closely enough to see if there are DMV tags on the license plate corners (government vehicles are exempt from needing the tags).

You've GOT to be kidding me. You're looking for a little sticker on the corner of their license plate just so you can go an extra 20 or 30 miles over the limit? All the while I'm sure you're giving your undivided attention to the actual task of driving the vehicle, I'm sure...

Sometimes, guys, it's just easier to stay closer to the limit. I know this opinion is unpopular around here, and I've had my share of tickets, but when it comes down to having to look for tiny stickers on the license plate, that's where I give up and say the cops have won.