Depends on which country.
The USA coin has it below head and above the date
between top of 7 and 2 numbers.
Other countries also issued 1 Dollar 1972 Silver >
Bahamas, Bermuda, Canada, Cayman Islands
The 1920 Half Dollar - aka - Liberty Walking - mint mark of "D" or "S" would be located on the reverse side, just to the left and above the "H" in half dollar.
The mint mark on a Barber Half Dollar is located on the reverse side right under the tail of the eagle.
Mintmarks are on the reverse above the letters DO in dollar
San Francisco
The U.S. didn't mint any silver dollars in 1920.
The mint mark on all Morgan silver dollars are located on the reverse of the coin near the bottom. Look above the "D" and "O" in the word DOLLAR
The mint mark on all Morgan silver dollars is located on the reverse side of the coin just above the letters "DO" in the word "DOLLAR".
The mint mark on any Morgan dollar is located on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
The mint mark on a 1936 Walking Liberty half dollar is located on the reverse [tails] side of the coin in the little "valley" just to the left of the word "HALF" near the edge of the rim.
If the coin has any wear the value is for the silver, about $8.50
They are still found in circulation, have no silver and are only face value
Exactly $100.