410 ILCS 635/9

All permits for farms, plants or stations as provided for in this Act shall be displayed in a conspicuous place for public view within or on the premises. A sticker or decal identifying the permit number must be displayed on the milk tank truck immediately adjacent to the manufacturer's identification plate. A milk hauler-sampler shall maintain upon his person his permit or renewal at all such times as he is operating a milk tank truck or collecting a sample. A certified pasteurizer sealer shall maintain upon his or her person his or her permit or renewal at all times during which he or she is testing a pasteurizer.