certified speedo

last summer i bought a 76 dart for parts. i just noticed it has a certified speedo. other than squad cars, what other cars would have had these? is it worth anything?

I remember someone on one of the boards having 2 of these cars that were squad cars. I believe there is a designation on the fender tag but I don't remember the code. I'm thinking they also had front and rear sway bars and they were really low production cars.
I think it would be a good idea to run the fender tag codes and see what shows up.
There is quite a following for squad cars if they are restorable.
Dallas