Special Delivery Stamp ~~ 1957

From MysticStamp.com ~~~~~>  "Special Delivery stamps were pre-payments added to the regular “lawful postage” for an extra service – immediate delivery of a letter within one mile of any special delivery post office.  These special post offices were those with free routine delivery service or in larger communities with 4,000 or more people.  

First available in 1885, the Special Delivery service was extremely popular.  At first, the service was available from 7 a.m. to midnight.  The following year, the hours changed from 7 a.m. to 7 p.m.  The service was so successful that in 1886, every U.S. post office began to offer Special Delivery."