Okay, so I found this 1994 penny that may or may not have a double die on the D mintmark. However my pictures are too blurry, but maybe someone here can enhance them? I have seen it before, and this really was the best picture I could take. I also wanted to show you guys this oddly colored 1973 penny. It is yellowish... I am 99% sure you all will say PMD, but I was curious as to what would cause this kind of coloration. Something chemical perhaps? Penny in question is pictured to the left of a regular penny for comparison.
Most of the gold and silver colored copper coins are left overs from certain chem experiments in lab manuals for middle and high school chem classes. People just toss them into circulation after the novelty wears off. http://www.metacafe.com/watch/1262456/make_a_gold_penny/ Also , the mint mark was added to the master die in 1990, so there should be no "doubled" mint marks due to the minting process. However, there can still be deteriorated die damage, or damage to the copper plating over the zinc core around the date or mint mark producing an effect which might be mistaken for a "doubling". Close up photos would probably get more specific opinions. Welcome to the forum! Jim