David Akers (1975/88): Although not as rare as the 1866-S No Motto, the 1866-S Motto still ranks as one of the rarest S-Mint issues, on a par overall with the 1860-S, 1861-S, 1862-S, 1864-S, 1867-S and 1868-S. With respect to condition rarity, the 1866-S Motto is in the top 10% of the entire Double Eagle series. Compared to all 204 $20 issues and not just those from the San Francisco Mint, the 1866-S Motto still fares well in terms of overall rarity ranking in the top fifth of the series. Almost all known examples of this date are in the VF and EF grades and a full AU is definitely rare. I have seen two uncirculated examples, the finest being the coin from the Harry Bass collection.
The Saddle Ridge Hoard of gold coins, discovered in northern California in 2013, contained several examples of the 1866-S With Motto $20, most of which were not ungradeable due to cleaning. However, the nicest coin, a PCGS MS62+, ranks as the finest example known of this date.
Saddle Ridge Hoard