Well, here's something I just kind of picked up out of pocket change and thought looked odd... Up near the top of the penny, in United States of America, the bottom halves of the words "States" and "of" are almost invisible, and can only be seen in the right light reflections. The first S is practically non-existent. Also, at the bottom on "One Cent" the top half of the "C" has the same effect, invisible unless reflecting the light. "us" is also just about missing in E Pluribus Unum.
