What service adds an extra layer of security by requiring a signature upon delivery?

The service that adds an extra layer of security by requiring a signature upon delivery is Signature Confirmation. This option is specifically designed to ensure that the recipient acknowledges receipt of the package, which provides proof of delivery that can be tracked. When a package is sent with Signature Confirmation, the mail carrier must obtain the recipient's signature when delivering the item. This not only verifies that the package was delivered but also enhances the security of items that might be valuable or sensitive, as it minimizes the risk of delivery errors or disputes regarding whether the package was received.

In contrast, Registered Mail, while it does provide a high level of security and can be tracked, does not specifically require a signature for delivery in all cases—it focuses more on safeguarding the contents during transit. Certified Mail also provides proof of mailing and delivery, but it typically sends a mailing receipt and may offer tracking; however, it does not provide the same level of security and signature requirement as Signature Confirmation. Express Mail, known for its fast delivery times, includes different features but does not inherently require a signature upon delivery. Signature Confirmation specifically addresses the need for a signature, making it the best choice for ensuring accountability upon receipt.