1979-S Type One

Note Filled Area In Mint Mark

1979-S Type Two

Note Clear Area In Mint Mark

1981-S Type One

Note That Clear And Filled Mint Mark
Does Not Apply To 1981. The Entire
Mint Mark Is Shaped Differently.

1981-S Type Two

Main Difference In Shape Is Upper "Arm" Of "S"
Looking Kind Of Like A Goose Neck.
Look Also At Center Of "S".
Type One Has A "Dip" In The Cross Bar
Type Two Is A Straight Line