The 1928-S Lincoln cent has two different style mint marks.
The first and most common is referred to as the regular 'S' mint mark.
The second variety is the Large 'S' mint mark. The Large 'S' mint mark is very scarce compared to the regular "S" mint mark cents.
It is not known exactly how much scarcer the Large 'S' is, since it really never caught on as a major variety, even though it is very easy to distinguish.
The 1928-S Large 'S' Lincoln cent is fairly difficult to locate in mint state grades, since I am only aware of less than five Large 'S' 1928-S Lincoln cents in mint state grades despite, seeing dozens of coins from this date and mint mark in uncirculated grades.
I would estimate that there are around 1,200 to 1,500 total 1928-S Lincoln cents in mint state grades in brown, red brown and red combined. Out of that figure, I would guess that there are about 50 to 100 Large 'S' Lincolns give or take and even then, most collectors, dealers and auction companies who do run into these coins, will probably never even realize that there are two different varieties. Therefore, making it an even scarcer variety to locate.
In circulated grades coins with a Large 'S' variety have sold for multiples more than one with the regular S. In mint state grades it is difficult to put a price, but I have seen one or two coins with the Large 'S' varieties in mint state grades sell for at least twice the price of a regular S mint mark.
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