Americans have always been extremely silly about this issue, stubbornly refusing to change even a single detail about their currency. As a result, it has always been the most easy currency to counterfeit. Untold thousands of legally blind people have been ripped off because they couldn't distinguish between a 1 and a 20.
Nearly every other country in the world has security features such as different colors, watermarking, threads, holograms and microscopic features hard to duplicate. And coins. But not the US.
Here's a post I found from Kuro5hin, "American Currency is Stupid" (written by an American)
http://www.kuro5hin.org/story/2006/12/31/45837/844Recently the US Mint outlawed the exportation or melting of pennies and nickels. Why? For one of the most hilarious of reasons: Pennies and nickels, in their zinc, nickel, and copper content, are worth more than a penny and nickel each! Not by much, but the world is experiencing a pinch in raw material costs (things like oil, paper, metals, etc.), as China, India, and other countries continue to soar as economic and industrial powerhouses, and this trend shows no sign of abating. So in the near future, melting pennies or nickels will probably net some enterprising souls a nice profit.
What's especially silly about this is that since money is really just an abstract expression of economic exchange and value, money can be anything. Making coins out of valuable metals is merely a throwback to an era when monetary exchange really needed to have intrinsic value to protect against currency scares and runs on banks. But this is an era which has long been passed in the world by over a century, we now use paper and plastic for most of our financial exchanges. The world economy is stable and interconnected enough that either the whole world melts down, or not. Therefore, faith in the international monetary system itself is more important than whether or not you have stockpiled enough South African Gold Krugerrands in your basement. If a country decides to use plastic coins, or seashells, or Rai stones, or Hello Kitty stickers, it doesn't matter. Currency merely needs to be hard or not worth it to counterfeit. That's all that is important.
snip!
As an illustration of how usability apparently means nothing to the US Mint, for a long time now, consider the silly decades-long saga of the American dollar coin. It would probably seem like a strange fact to modern Americans (since hardly anyone uses them, and when they get them in their change, it is like getting an artifact from Alpha Centauri), but for most of American history, there have been dollar coins. At first they were huge wonky things. Which was fine, since back then one US dollar really meant something important, back when you could buy candy bars for a penny. These hulks were revived in the 1970s as... the same huge wonky things. But by the 1970s, dollars didn't command that much respect to weigh down your pocket by five pounds. And then, someone at the mint grew half a brain cell. Emphasis on half a brain cell: "As inflation affects the value of our coinage, more and more people use bills instead of coins, so let's join most of the rest of the world and devise a dollar for wider use as a coin."