Every country has peculiarities of its specialization. The Germans have coil numbers printed on the back of stamps and collect their coils in strips of eleven to prove that the stamps didn't come from a sheet which was printed with rows no larger than ten. The French collect gutter pairs with plate numbers, called millisimes. The Swedes measure the perfect centeredness of their socked-on-the-nose cancels. But no country collects their revenue stamps like the United States. No country includes such a broad array of revenues in the specialty catalogs as are listed in the Scott US Specialized catalog. No country lists Privately issued revenues such as the US Match and Medicines. And finally, no country has so many or so avidly collected Duck Stamps. The Hunting Permits, or Ducks, as they are called  are issued each year and have been since 1935 to pay the Federal tax on Duck Hunting. They are probably the greatest crossover philatelic item. More non stamp collectors collect Duck stamps (as part of their passion for duck hunting) than collect any other kind of philatelic item. It is a tribute to the passion and political power of duck hunters that  the price of a duck stamp has not gone up in over thirty years. Hunting taxes are user fees which government has been hiking up for years so as to not have to raise tax rates. But America's millions of hunters in every House district in the land have seen to it that their hunting taxes have remained low. Duck stamps are among the most popular sub specialty in US philately and a complete mint set can be assembled for about $1500 mint hinged, $2000 NH and $500 used.