The 1866-S Half Dollar has a hefty mintage of nearly a million coins, but because of the remote location of the San Francisco Mint, the survival rate of high-grade examples is smaller than coins from the Philadelphia Mint with similar mintages. For example, the 1866 With Motto Half Dollar has a smaller mintage than the 1866-S With Motto, yet the number of certified examples of the former is fifty percent higher than the latter. This explains why Mint State 1866-S With Motto Half Dollars command a substantial premium over the 1866 With Motto.
This date comes with a tiny mintmark. Most examples are well struck in the centers, but often show weakness in the stars on either side of Liberty's head.