The Rules are pretty basic. The kids try to find interesting things OUTSIDE of the car, and if they're the first person to see something cool, they get a jelly bean! Of course, Dad and I are the ULTIMATE judges of what is really cool, and (sorry Limber) signs and trees DO NOT count! I painted a jar with the words "I Spy, See my Eye," since that's what Bushkin (2) says whenever we play I Spy.
This has really opened my kids eyes to see the beautiful things around them. However, I caution any readers who use this idea. It can be irritating when your 3 and 5 year old yell out every half a second whenever they see a sign; "look, a sign with a bear on it," "Look, a sign with a letter A on it," "Look,....you get the idea! But it's worth putting up with the silly stuff (which they don't get rewarded for), since we found a way to get them to interact with the world around them.