From the USPS website
“The USPS offers a service called Signature Confirmation that gives shippers extra peace of mind by requiring a signature from the recipients of their packages. Although USPS Tracking proves that a package was delivered to a particular address, Signature Confirmation proves that it was actually received by the intended recipient or his agent.
Signature Confirmation costs $3.15 when purchased at a Post Office, and $2.65 when purchased electronically using online postage services such as Stamps.com. Signature Confirmation provides shippers with the name of the recipient as well as the delivery date, time, and location; a copy of the recipient’s signature will also be faxed, mailed, or e-mailed to you upon request. Delivery status information is available for one year after the date of delivery, and can be accessed online or by phone.
Shippers may purchase Signature Confirmation with the following mail classes and services: First Class Mail (packages only), Priority Mail, First Class Package Service (packages only), Media Mail (packages only), Collect on Delivery, Insured Mail, Registered Mail, Restricted Delivery (if COD, Registered Mail, or insured for over $200) and Return Receipt (if COD, Registered Mail, or insured for over $200).
To ensure receipt by a specific person (rather than that person’s agent), use Restricted Delivery in conjunction with Signature Confirmation. This requires the recipient of your package to positively ID himself before the USPS carrier will deliver the package. ”