It seems that the words post office,registered mail,certified mail,priority mail express,and signature confirmation are trade marked. : r/mildlyinteresting
Kuwait Ganzsache Einschreibe Umschlag 40 c Segelschiff Registered Letter Ganzsache postal stationery | MA-Shops
How to Send a Registered Letter: 11 Steps (with Pictures)
Keep Track of Your Postal Items | Western Cape Government
How to Send a Registered Letter: 11 Steps (with Pictures)
Registered Post Office Department Envelope, July 6, 1898] - The Portal to Texas History
Registered letter hi-res stock photography and images - Alamy
Guide to USPS Certified Mail | Red Stag Fulfillment
HOW TO: Send A Registered Mail At QC Post Office - The Momma Chronicles