(1920) P50c Pilgrim Tercentenary, Silver, J-C1920-2, Pollock-7030 MS

Both the obverse and reverse designs are similar to those adopted for the regular issue 1920 Pilgrim Tercentenary commemorative, but with subtle differences. This is a controversial issue, its background expertly related on the uspatterns.com website:

These were originally offered as lot 295 in Christie's London 12/8/87 sale in an original frame as "presented by the engraver Cyrus E. Dallin and signed on the bottom, Cyrus E, Dallin, 1921". The frame contained 3 silver, 2 brass and 2 uniface pieces...

An article on these appeared in the January 20, 1988 edition of Coin World which declared all of these to be fake as there are differences in the appearance of these versus those struck at the Mint in 1920 and 1921. On the obverse, the obverse stars and periods are larger and the clasp on the book is stronger. Governor Bradford's eye also appears to be closed and the motto 'In God We Trust' is uneven and not level. On the reverse, the 92 in 1920 is higher, the position of the bowsprit with relation to the M in PILGRIM is wrong and the configuration of windows is different.

Today, these are believed to have been prototypes privately struck by or for Dallin prior to the final design that was struck at the Mint.

Source: Stack's Bowers