The Evergreen museum claims that this is the fifth S-51 built and this appears to be correct, meaning that it was one of the first commercially operated helicopters in 1946 as NC92803 - see other picture. After bankruptcy of the pioneering HAT company it was sold to the USCG as 233, later 1233.

Experimental air mail delivery in Brooklyn. We found the location doing a reverse image search for the church. HAT was the first commercial helicopter operator. The S-51 appears to be NC92803, delivered to the company from Camden, New Jersey in September 1946. HAT filed for bankruptcy in October 1947. NC92803 went to the US Coast Guard as an HO3S, 233. Now preserved in the Evergreen museum, Oregon. Photo from: Nationaal Archief (Netherlands)