As for cop cars and efficiency, check out this article: (can't post links yet) cleanmpg.com/forums/showthread.php?t=39994]NYPD to take delivery of 50 Chevy Volts - CleanMPG Forums(can't post links yet)
Also as to the whole idea about cops, judges and revenue, the state police in my state actually say on their website that the highway patrol's revenue doesn't come from tickets. As the OP stated he was on a highway exit ramp (I think) I don't see how that particular argument applies. A police officer would not have pulled him over for the sake of writing a ticket and making money, it just doesn't work that way. Now I don't know about specific counties or cities, but that is how the state police operate.
Now to comment on the actual subject matter intended by the OP. Since I started hypermiling and driving a little more slowly I've been getting some more interesting reactions from other drivers. Pretty much the same stuff as everyone else, raised fingers and fists, questioning gestures, and irate/erratic driving. I get passed a lot even when no passing lane exists.
At this point I have started to just assume I'll be passed and I drive my passenger side as close to the right of my lane as possible. Usually it encourages a pass and it's somewhat safer I guess. I'm always interested to see the reactions of people in their cars, especially since I used to drive aggressively. Now I get to see what it was like for all the defensive drivers I used to pass for no reason.
Just a few days ago I got passed on the left on a 5-lane road and received the venerable raised fist award. Several blocks ahead, I was right next to this wonderful average american driver, so I honked, waved and smiled
I'm glad to have seen this post as I never would have thought to put a sign up in my rear window. That is a really smart, good and defensive idea.