What this coin looks like (obverse, reverse, mint mark location, special features, etc.): There were a few major varieties of the 1809 Classic Head Half Cent (Penny). The most common is the normal date variety which does not feature any errors in the 1809 date. The normal date variety is depicted above in the example image.
One major error is the 1809/9 (or 1809/6) overdate variety. This features an 1809 date struck over an inverted date. This results in a "9" struck over an inverted "9" although the inverted "9" simply looks like a "6" - hence sometimes known as 1809/6. Parts of the underlying inverted "9" are seen within and around the overlying "9" as depicted below in the example image of the coin:
Another major variety features a small circle within the "0" in the 1809 date. This was the result of a large date struck on top of a smaller date which resulted in parts of the smaller zero showing up within the big one. This is depicted by the arrows in the example image of the coin below: