New York World's Fair 1939

Obviously a philatelic item, specially prepared, but can anyone tell me if there is some special significance to the date/stamp/cancel combination? Slogan reads "Railway Mail Service".

Certainly is! May 16, 1939 was the First Day of Issue of the stamp (C24). My old 2002 Scott catalog suggests that "only" 68,634 were produced and back in 2002 it was "valued" at $47.50 (of course, that's catalog value and is further diminished by the fact that it has no cachet and is on a legal size envelope.) However, to it's credit, the cover looks to be a clean example with the RMS cancel, which would add to it's desirability to an airmail collector. Certainly should have a value above a run-of-the-mill first day cover.

(NOTE: 2010 catalog value for the item remains unchanged.)

Nice cover, the railroad exhibit at the fair contained US railway Post Office Car, NYC 4868. This was a fully operational RPO that was used to help with the high volume of outgoing mail from the fair. I have seen other FDC of this issue but cannot recall the RPO cancel on them. Additionally, most have the New York cancel rather than the world's fair cancel.

Great looking cover!

I am surprised! This was just one of those bottom of an auction box things that I don't really collect but looked interesting. I believe I have noticed one or two threads with references to hoarding but, of course, would never think of applying the criteria to myself. And to think, there are only 68,232 still unaccounted for.

Thank you for the information and I post a companion piece with a different corner cancel and an added commemorative.