What must be marked above the address when using special services?

When utilizing special services for mailing, it is essential to clearly indicate the service type above the address on the envelope or package. This marking informs postal workers about the specific service associated with the mail item, such as certified mail, registered mail, or insured mail, allowing them to handle the delivery process accordingly and ensure that the item receives the appropriate attention and care throughout its transit.

Using this marking system helps streamline the mailing process and enhances the security and tracking capabilities associated with special services. For instance, if you mark an item as "Certified," it indicates that a delivery confirmation is needed, which will guide postal employees in managing the item properly. This clarity facilitates efficient processing and reduces the chances of errors, ensuring that the mail arrives at its destination safely and in a timely manner.

In contrast, while a return address, sender's name, and special instructions are important for different reasons, they do not specifically convey the type of service being utilized, which is crucial for the treatment and handling of mail under special services.