<Table> Walking Liberty half dollar <Tr> <Td_colspan="2"> United States </Td> </Tr> <Tr> <Th> Value </Th> <Td> 50 cents (0.50 US dollars) </Td> </Tr> <Tr> <Th> Mass </Th> <Td> 12.50 g </Td> </Tr> <Tr> <Th> Diameter </Th> <Td> 30.63 mm </Td> </Tr> <Tr> <Th> Thickness </Th> <Td> 1.8 mm </Td> </Tr> <Tr> <Th> Edge </Th> <Td> reeded </Td> </Tr> <Tr> <Th> Composition </Th> <Td> <Ul> <Li> 90% silver </Li> <Li> 10% copper </Li> </Ul> </Td> </Tr> <Tr> <Th> Silver </Th> <Td> 0.36169 troy oz </Td> </Tr> <Tr> <Th> Years of minting </Th> <Td> 1916--1947 </Td> </Tr> <Tr> <Th> Mint marks </Th> <Td> D, S. Located for 1916 and some 1917 pieces on obverse to right of Liberty just under the letters "Tr" in "In God We Trust", later issues on reverse at lower left, under the tree . Philadelphia Mint specimens lack mint mark . </Td> </Tr> <Tr> <Th_colspan="2"> Obverse </Th> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Th> Design </Th> <Td> Lady Liberty walking and holding branches; United States flag over shoulder </Td> </Tr> <Tr> <Th> Designer </Th> <Td> Adolph A. Weinman </Td> </Tr> <Tr> <Th> Design date </Th> <Td> 1916--1947 </Td> </Tr> <Tr> <Th_colspan="2"> Reverse </Th> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Th> Design </Th> <Td> A bald eagle rising from a mountaintop perch </Td> </Tr> <Tr> <Th> Designer </Th> <Td> Adolph A. Weinman </Td> </Tr> <Tr> <Th> Design date </Th> <Td> 1916--1947 </Td> </Tr> </Table> <Tr> <Td_colspan="2"> United States </Td> </Tr>

Where is the mint mark on a walking liberty half-dollar