Gordon Wrubel: Quickfinder Notes: Proof expert, John Dannreuther, points out some positional differences involving the point of the shield and the 1&8 of the date to the denticles, to determine Proof versus Mint State status. There is also an easy "tell" on the reverse. Look at the "In God We Trust" SCROLL above the eagle. If the SECOND, RECESSED, UNDULATION from the LEFT has been polished down so that only the two THIN OUTER BORDER LINES remain, the coin is a Type II proof. A vast majority of 1880 proofs will have this reverse. On Mint State coins, the second undulation is FULL and COMPLETE. This difference can be seen even on worn specimens.
We have noted two "full scroll" Proof exceptions to this rule. One is the very rare "proof only" issue which uses the Type I Reverse of 1872. This die is identified by a DIE CUT from the LEFT BORDER of the SHIELD into the FEATHERS. The second exception is a Type II reverse. This die is easily recognized by TWO RAISED LUMPS on the first undulation at the LEFT END of the SCROLL and more lumps at the CENTER of the SHIELD.