This is the only stamp ever issued by the U.S. Post Office Department solely for Certified Mail service. The service continues, but any form of postage may be used. Certified Mail service was for use on first-class mail for which no indemnity value is claimed, but for which proof of mailing and proof of delivery are available at less cost than registered mail. The matter receives one receipt, and the addressee signs another when the mail carrier delivers the letter. The second receipt is kept on file at the post office for six months. The Certified Mail charge is in addition to regular postage.