The U.S. minted 2 types of $20.00 coins, but George T. Morgan did not design them. The Liberty Head (1849-1907) was designed by James B. Longacre. The mintmark is on the reverse under the eagle. The Saint-Gaudens (1907-1933) type was designed by Augustus Saint-Gaudens and has a obverse mintmark above the date.
If you know it's a 1921 "S" Morgan you found the mint mark
Please check again and post a new question. The C mint mark was only used on gold coins minted from 1838 to 1861. Your coin should either have no mint mark, a D, or an S.
For coins dated 1906 to the present, it means the coin was made at the Denver Mint. A "D" mint mark on an old (1838-1861) gold coin means it was made at the long-closed gold coin mint at Dahlonega, GA.
To determine where a coin was minted it is necessary to locate the mint mark. This mark is a small letter or letters located somewhere on the coin. For the Morgan Dollar, this mark is located on the reverse [tails] side of the coin just above the letters "DO" in the word "DOLLAR". For the Carson City mint the mark is a "CC". {quotes are mine}
The mint mark (if it has one) on all Morgan (1878-1904 & 1921) silver dollars is on the reverse of the coin, just above the letters "DO" in dollar.
Sorry no Carson City mint marks in 1887 on a Morgan dollar. Look at the coin again.
The mint mark (if it has one) on all Morgan silver dollars is on the reverse of the coin just above the letters "DO" in dollar.
According to coinbrag.com the mint mark is located on the obverse over the date.
mint mark is to the left of the value on the reverse.
The mint mark on a $5 gold coin from that era is on the reverse (tails) side, just below the eagle.
The mint mark on a Morgan dollar (if any) will be found on the reverse of the coin under the wreath between the "D" and "O" in "DOLLAR".
$680 to $27,500 depending upon the mint mark and the condition of the coin.