The U.S. didn't mint any silver dollars in 1920.
As of 3 April 2014, one is worth just over $15 for the silver. For a more specific answer, ask about a specific coin, including the date, mint mark, and condition.
1922 dollars were struck only at Philadelphia (no mint mark), Denver (D) and San Francisco (S). All are worth about $15. The U.S. has never had a "K" mint mark. My guess is that you're seeing the designer's monogram or some other marking.
1981
1923 Peace Dollars are so common, circulated coins with no mintmark sell for 30.00-$37.00. Typical uncirculated coins are $39.00-$45.00. The actual value depends on the grade of the coin.
The 1921 Morgan is the most common of all and regardless of mint mark, circulated coins sell for $14.00-$25.00 Mint state coins sell between $30.00-$40.00 and as all ways value depends on the grade.
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.
Mintmarks are on the reverse above the letters DO in dollar
San Francisco
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 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 any Morgan dollar is located on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
1899 would make it a Morgan dollar. The mint mark is located on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
By the mint mark on the reverse of the coin, but silver dollar coins with no mint mark are made in Philadelphia
1928 makes it a Peace dollar. The mint mark is located on the reverse (tails) side, below the word "one." D for Denver, S is San Francisco, and no mark is Philadelphia.
above the DO in dollar on the back :]
The mint mark on any Morgan dollar is on the reverse above the letters DO in dollar.
The mint mark is located on the eagle side of the coin and is between the word " fine " and the eagle.