Unlisted Hand Drawn and Painted Cachet by Elton Mancell
Art Cover Society (ACE #16.) (Probably One of a Kind)

The addressee Victor H. Van Horn was ACE#2. He co-founded ACE along with Leonard Turley. The "16" at lower right is Elton Mancell's number.  This cover was originally a part of the Van Horn collection, which was purchased virtually intact by the noted cover dealer (and good friend) Robert Motelow.