Most collectors are unaware of this very scarce Official Carrier stamp. LO1 was issued by the U.S. Post Office as part of the Issue of 1851. Semi-Official Carrier Stamps paid for local carriers to deliver a letter to or from a post office. At that time, ordinary U.S. postal rates only secured delivery between post offices – not to your address. The U.S. Post Office issued this “Official” carrier stamp in an attempt to standardize the carrier service. LO1 was used mainly in the cities of Philadelphia, New York, and New Orleans.