Sweden Three Skilling Banco
Most expesive single postage stamp sold in auction is Sweden Three Skilling. In 1996 the stamp was sold to an anonymous collector for $2.3 million at auction. The three skilling stamp was issued in Sweden in 1855. This stamp was printed on yellow colored paper instead of the usual green color.
Post Office Mauritius
The Mauritius Post Office stamps were issued by the British Colony Mauritius located in the Indian Ocean in September 1847. A local watchmaker from the capital city of Port Louis engraved the words Post Office instead of the correct words Post Paid on the stamps. About 30 copies of these stamps have survived and they are valued at between $600,000 or more
credit: Philatelic Library
U.S. Franklin Z-Grill
Only 2 copies of this stamps are known to exist. Stamps were issued in 1867. These stamps show a portrait of Benjamin Franklin and are embossed with a Z-Grill – being a pattern of tiny squares embossed into the paper and visible on the back of the stamps. The purpose of the “Z-Grill” was to permit the canceling ink to be absorbed into the stamp paper thus preventing those who wanted to cheat the post from washing out cancellation marks. An 1868 1 cent “Z-Grill” stamp sold for $930,000 in 1988.