File:Parcel Post 1912-13 issues.jpg - Wikipedia
National postal museum hi-res stock photography and images - Alamy
U.S. Special Delivery (postal service) - Wikipedia
National Postal Museum
America's Bicentennial – The U.S. Post Office.
Q4 - 1913 4c Parcel Post Stamp - Rural Carrier - Mystic Stamp Company
National Postal Museum
Parcel Post Stamps National Postal Museum
The postal museum hi-res stock photography and images - Alamy
Parcel Post Map National Postal Museum
Q1 - 1912-13 1c Parcel Post Stamp - Post Office Clerk - Mystic Stamp Company
National Postal Museum
National postal museum hi-res stock photography and images - Alamy