What does the USPS use to indicate the class of mail?

The USPS uses postage stamps or labels with the service type indicated to denote the class of mail. This system provides a clear and immediate visual representation of the type of service that has been purchased, such as Priority Mail, First-Class Mail, or Media Mail. By looking at the stamp or label, customers can easily determine the expected delivery time and additional features such as tracking or insurance that come with each class.

In contrast, while unique tracking numbers can give information about the item's journey, they do not indicate the class of mail at a glance. Color-coded boxes are not an official USPS method for classifying mail, as they may be used internally or for packaging but do not represent the service type. Delivery receipts can confirm that a package was delivered but they do not indicate the class of mail used for shipping. Thus, the use of stamps or labels is the most effective and direct way for the USPS to convey the class of mail.