When Liberty Walking silver half dollars debuted in 1916, mint marks were on the obverse below the motto in god we trust. Partway through 1917, the marks were relocated to the reverse - the reason given by the U.S. Mint that "the obverse mint mark had the appearance of a defect in the die and was entirely too prominent." Offered here is the 1917-S half dollar with the "S" mint mark on the reverse below the pine sapling - an important series issue!