5c Douglas Plane over Sosa Hill plate proof
Certified plate proofs are the last printed proof of the plate before printing the stamps at the Bureau of Engraving and Printing. These plate proofs are each unique, with the approval signatures and date. For postal scholars these plates provide important production information in the plate margin inscriptions, including guidelines, plate numbers, and initials of the siderographer, or person who created the plate from a transfer roll.
Subject: Douglas Plane over Sosa Hill, Canal Zone Air Mail
Color: greenish black