Mint marks on walking liberty half dollars

During the first year (1916) and part of the second year (1917) of production, a mint mark: D for Denver or S for San Francisco appears on the obverse of the coin below the words "In God We Trust.." In the later part of 1917 and for all subsequent coins, the mintmark appears on the reverse near the edge of the coin to the left of the eagle. Coins without mintmarks were minted in Philadelphia.