Bridging WWI & WWII

Okay, I have no idea of value here or even what category to place this under. This is a one-of-a kind folk art, I guess - envelope. It's a really great design and artwork - on the cover of a letter. It was originally framed for the artwork. But after digging around online here's the cool part I discovered.

First, the date it was postmarked - april 15, 1917 is highly significant. It's the day that Woodrow Wilson gave his 'make the world safe for democracy' speech in which he announced to the American public that the US Congress had passed the declaration of war - and that the US had entered WWI. Hence the incredible patriotism of the piece.

Here's where it get's fun - the recipient of the letter - C.H. Swickerath - is the father of Carl H. Swickerath - a highly decorated officer in WWII and the very good friend of Audie Murphy. Carl spoke at Audie's funeral and visited his grave often. Carl is buried directly in front of Audie at Arlington Cemetery.

So how often does a piece come along that pulls together both great wars and has some incredible artwork on it? I'm thinking not that often. C.H. Swickerath was a sign painter for Mail Pouch, and although I don't know the actual artist - it could have been one of his sign painter friends - which would explain the great artwork.

all that said, does anyone have a clue as to value, (it's not pristine - it has some molding which you can see in the picture)