The phrase "stamp of approval" may take on a little more significance when you realize just how special you have to be to receive recognition on a stamp. Around the world, countries have saluted their greatest artists with recognition on a stamp, yet there are still legends who have not been recognized as of yet.

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In the U.S., the U.S. postal service started a series back in 1993 honoring some of the pioneers of American rock 'n' roll. Included in that series are Elvis Presley, Ritchie Valens and Buddy Holly among others. In addition, legends such as The Beatles, John Lennon, Jimi Hendrix and Janis Joplin have made the cut, but when you look at the history of rock 'n' roll, there are still many deserving acts who don't have a stamp stateside.

But other countries have stepped up in that matter. AC/DC has been saluted in Australia, the U.K.'s Royal Mail has chosen to celebrate some top acts by sharing their album covers on stamps. And in Finland, a few years back, they honored the country's top hard rock and metal acts with stamps.

Who's got a stamp? You might be surprised. Check out some of the history of rock and metal bands on postage stamps below.

24 Rock + Metal Postage Stamps