1979-S And 1981-S Ty-1 & Ty-2 MM Differences

Check this one out in particular on how to tell the difference between the 1979-S and 1981-S Ty-1 and Ty-2 Mintmarks. This used to be a hand-out that Numismatic News passed out at shows in the 1980s. I still have a small handful of them.
Note that clarity of the mintmark has nothing at all to do with which variety it is, contrary to what some will tell you.
A mintmark punched into a die hard can appear "filled" - even on the Ty-2 MMs. Look for the differences in the shapes of the loops, etc., not clarity -- though this is far less of an issue with the 1979-S as the Ty-1 is very obviously deformed from long use.

Another post showing a different document earlier today was incorrect.