USPS Test Marketing New Service – First Class Tracer
To make it easier for customers to track envelopes with First Class Mail postage, the U.S. Postal Service is testing a new service called First Class Tracer at 50 retail locations near Washington, DC, Maryland and Virginia.

The First Class Tracer service uses scanning technology to let customers keep tabs on greeting cards, postcards and personal/business letters as they go through the mail stream.
How First Class Tracer Works:
To use First Class Tracer, customers apply an adhesive barcode to the mailpiece directly below the postage stamp area on their envelope. Each barcode has a unique number that can be tracked on the usps.com site, similar to how you would use track a package using Delivery Confirmation or Signature Confirmation. The barcode also includes a unique Quick Response code that can be monitored on smartphones or other mobile devices.
First Class Tracer is being test-sold in two packages — a 5-label pack for $1.99, and a 10-label pack for $2.99.