The vehicle certification label aka the "door tag" is a sticker that is affixed to either the rear face of the driver-side door on hatchbacks and coupes OR the driver-side door latch post on convertibles. The sticker contains information about when and how the car was built. Below are sample door tags and a brief explanation of the codes on them. Door tags can now be decoded here: http://foxchassis.com/decoders/doortag

1. DATE - Scheduled (estimated) date that the vehicle was to be manufactured. The actual manufactured date is usually the same but not always.
2. GVWR - This is NOT the "curb" weight of the vehicle. Gross vehicle weight rating is the maximum allowable total weight of the vehicle (chassis and body, drivetrain, fluids, fuel, and accessories) AND driver, passengers, and cargo.
3. FRONT GAWR - Front gross axle weight rating is the maximum allowable weight that can be supported by the front "axle" (front suspension)
4. REAR GAWR - Rear gross axle weight rating is the maximum allowable weight that can be supported by the rear axle.
5. VIN - Vehicle identification number is a unique serial number to identify the chassis.
6. TYPE - Indicates the type of vehicle it is.
7. Fnnnn/Rnnnn - Accessory reserve load is the maximum allowable amount of weight of extra equipment or accessories that can be added (permanently or removable) over the Front and Rear axle before that respective axle is overloaded.
8. EXTERIOR PAINT COLORS - Color that the body was painted. A second two-character code (not shown) would indicate type and color of a vinyl roof (1978-79) or color of lower or special tu-tone paint (1980-92).
9. DSO - District sales office that the car was ordered through. An additional four digits (not shown) would indicate a special order.
10. BODY - Corresponds with the line/series/body code in the VIN (3rd and 4th characters 1978-80, 6th and 7th characters 1981-92).
11. VR - Type and color of vinyl roof or carriage roof (1979-82), or color of convertible roof (1983-86).
12. MLDG - Type and color of the bodyside molding and the color of the stripes in the molding.
13. INT TRIM - Type and color of the seats and the rest of the interior. A third letter (not shown) indicates a trim "deviation".
14. A/C - Indicates factory-installed air conditioner (through mid-1983) OR color of hood/fender/hatch/trunk decals (mid-1983 and later Capri RS or Mustang GT) OR bodyside pinstripe color (mid-1983 and later). "A/C" changed to "TAPE" in 1986.
15. R - Type of factory-installed radio.
16. S - Indicates a factory installed sunroof or T-roof, or neither if blank.
17. AX - Ratio of the rear axle gearset AND type of differential (conventional or limited-slip).
18. TR - Type of transmission
19. TR (last four) - Left Front, Right Front, Left Rear, and Right Rear coil springs.