The 1856-S $2.50 is close in rarity to the 1857-S, but it is almost twice as common as the 1859-S. Approximately two to three dozen Mint State examples are known, most of which grade from MS61 to MS64. The finest example is a PCGS MS67 that was recovered from the wreck of the S.S. Central America -- it is but one of a tiny handful of MS67 Quarter Eagles from the pre-Civil War era. This date usually comes with a nice frosty luster.
The mintmark on the 1856-S Quarter Eagles appears in at least two widely different position. Most often, the mintmark is wedged tightly into the area between the eagle's right talon (viewer's left) and the fletch of the arrow. Other times, it is seen almost touching the upper left serif of the D.