It does appear to be a RPM. The two listed on coppercoins that is like this have also a doubled die on them as well.
http://coppercoins.com/lincoln/dies...ie_state=lds
http://coppercoins.com/lincoln/dies...ie_state=mds
But the locations of the mint marks look different than Joe's coin. The date isn't filled, but the die is actually crumbling away in the insides of these devices. But they do serve as marks for certain die states. But I don't think either of these two are the same die that created Joe's coin.
http://coppercoins.com/lincoln/dies...ie_state=lds
http://coppercoins.com/lincoln/dies...ie_state=mds
But the locations of the mint marks look different than Joe's coin. The date isn't filled, but the die is actually crumbling away in the insides of these devices. But they do serve as marks for certain die states. But I don't think either of these two are the same die that created Joe's coin.



















