Mercury is a Roman god, known as the god of trade, profit and commerce. He is very similar to the Greek god Hermes and he is known for his winged cap and winged feet. Mercury was the messenger of Zeus. The wings crowning his cap are intended to symbolise liberty of thought.
Newspaper stamps are issued specifically for prepayment of mailing rates for newspapers, periodicals and printed matter.
K.u.K. (Kaiserliche und Königliche) Feldpost = Emperial and Royal field post.
Kaiserliche und Königliche (Emperial and Royal): The Austro-Hungarian empire was ruled by a person (Franz Joseph) who was emperor for Austria and king for Hungary.