Adult Signature Domestic Use Only Electronic Only Do you need to ensure delivery is to a person who is 21 years of age or older? Use Adult Signature service. There are two types of Adult Signature service: Adult Signature Required service allows you to restrict delivery to a recipient 21 years of age or older. Adult Signature Restricted Delivery service allows you to restrict delivery to a specific recipient 21 years of age or older. There is no form for Adult Signature service. You can purchase it online through Click-N-Ship, at usps.com, or through an authorized PC Postage vendor. Adult Signature service uses the Intelligent Mail package barcode (IMpb). Additional information: Available for Priority Mail Express, Priority Mail, First-Class Package Service*, Parcel Select, and Parcel Select Lightweight items. Pay the applicable extra service fee.