To get one of these:
You must have your vehicle in your garage, and you must have a fuel log.
Use this link: "http://ecomodder.com/forum/fe-graphs/sig
XXXXa.png"
Change "XXXX" to your vehicle's ID, which can be seen in the address bar of your car's garage page. For my Insight, for instance, I've bolded the vehicle ID here:
"http://ecomodder.com/forum/emgarage.php?do=details&vehicleid=
8464"