There's no such coin. The last Peace dollars minted for circulation were dated 1935. The last Peace dollars ever minted were dated 1964 but they were never distributed.
There is no mint mark on the 1921 Peace dollar because they were all minted in Philadelphia and thus carry no mint mark.
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.
If it has one, it's just above the eagles tail near the rim.
It's on the back below the ONE no mark means Philadelphia.
No Mintmark just means it was made in Philadelphia.
It's on the reverse between the tip of the eagles tail and below the word one near the rim.
If it has one, it's on the reverse just above the tip of the eagles tail near the rim.
The mint mark on any Morgan dollar is on the reverse above the letters DO in dollar.
The 1928 Philadelphia Peace Dollar has no mint mark, indicating it was minted in Philadelphia. A normal 1928 Peace Dollar would have a D or S mint mark denoting it was minted in Denver or San Francisco. The absence of a mint mark on the coin indicates it is the Philadelphia Mint version.
This is a Peace dollar. The mintmark for Peace dollars is located on the back to the left of the eagles wingtip. Keep in mind it may be blank if it was made at the Philadelphia mint.
It's the monogram of the designer, Anthony de Francisci. All Peace dollars have it.
If the 1928 Peace dollar has no mint mark, circulated coins have retail values of $275.00-$430.00 depending on the grade.