The blue lines show where the sheet is pre-cut, they are not printed.
It is to suit the Classic Airships S.S. Zero model in 1:350 available in two parts in the Shapeways marketplace: go to Shapeways, click on Marketplace and enter AMLJSNRJ4 in the search bar to bring up the Envelope or MVLY9KEJV to bring up the Fine Detail Parts kit.
I recommend always using a good decal softener such as either Revell "DECAL Soft” or Tamiya "MARKFIT STRONG".
International letter post (without tracking) is INCLUDED IN PRICE
Nominal size: 105 mm x 75 mm