Oregon Revised Statutes Oregon Vehicle Code § 825.212

(1) Prescribe such methods and means as the department determines to be necessary for checking, verifying and ascertaining the number of miles traveled by each motor vehicle operated by for-hire carrier and private carrier and insure that the mileage charged for is computed on basis of extreme mileage traveled.

(2) Prescribe distinguishing marks, such as signs, colors, lights, tags and plates as may be convenient or necessary for distinguishing classes of carriers or for protective or regulatory purposes; but not inconsistent with the Oregon Vehicle Code.