Postal ephemera collectors might be interested to know that new Certified Mail and Registered Mail labels will be available in January 2014 in order that they NOT have a tracking barcode.
They are designed for use on packages that already have an Intelligent Mail package barcode label, so there's only one barcode per shipment. (Apparently the long-used Certified Mail and Registered Mail labels with barcode will still be available for use on mail that doesn't have another package barcode label on it.)
Here's an image of the Certified Mail variety (Label 3800-N):
