Milled or lettered edges have been used since the 17th cent. to discourage the removal of slivers of metal, especially from gold or silver coins. As per "Columbia Encyclopedia"

Die rotation refers to the location of the "top" of the coin's image when the coin is turned over. For example, if you look at the obverse of a U.S. penny with Lincoln's head right-side up, and then turn the penny over from top to bottom, the building should be right side up on the reverse. This is called "coin alignment."

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Upside Down Heads on Coins
Almost every day we get asked about coins described as having "the head upside down", or at least the two sides of the coin the wrong way round compared with "normal" coins. This is because many modern coins are struck with "Medal Alignment" instead of "Coin Alignment".

Impossible to have Head Upside Down
It is actually impossible to have a coin with the head upside down. This is because the head side of the coin is defined as the main side or obverse of the coin. The other side is termed the reverse or secondary side of the coin. Because of this it is never the head which is upside down, it is always the reverse which is upside down. For some strange reason, almost everybody finding such a coin describes it as having its head upside down, we don't know why.

Inverted Designs
The positions of the obverse and reverse relative to each other are known as the alignment of the coin. Since the very first coins, it has been quite common for the two sides not to be perfectly aligned with each other, however there are two common alignments, These are known as "coin alignment" and "medal alignment".