What this coin looks like (obverse, reverse, mint mark location, special features, etc.): There were a few major varieties of the 1809 Capped Bust Half Dollar. The major varieties deal with the various designs on the edge of the coin - although there are many Overton sub-varieties. All varieties have the words "FIFTY CENTS OR HALF A DOLLAR" along the edge of the coin. The most common variety has smooth surfaces between the words with no special markings.
The US Mint decided in 1809 to experiment and test out other various designs to use on the edge of the coin. One variety is the "III" edge - which consists of vertical hashes between the words on the edge. An example of this is depicted below (Source of example image is courtesy of NGC Coin):
The other major variety features the "XXX" edge - which consisted of twisted X's between the words. This is depicted below in the example image (Source of example image is courtesy of NGC Coin):