For the first time ever, Proof American Silver Eagles have been released with edge lettering. For commemorating the 30th anniversary of the American Eagle, the 2016 Proof American Silver Eagle has been designed to have lettering in the edges where it is usually reeded. Though rare, edge lettering in coins is not a new phenomenon. Some of the earliest American coins have edge lettering. Modern coins like the Presidential $1 coins and the Native American $1 coins also have edge lettering.
Early edge lettering coins
Flowing Hair Half Dollar/Dollar
The Flowing Hair Half dollar and dollar were released in 1794. Both had the same design done by Robert Scot, the first Chief Engraver in the US Mint. The edge had the lettering ‘FIFTY CENTS OR A HALF DOLLAR’ with decorations between the words for the Half dollar. For the dollar, the edge had the lettering ‘HUNDRED CENTS ONE DOLLAR OR UNIT’ with decorations between the words.
Draped Bust Half Dollar/Dollar
The Draped Bust Half dollar and dollar were released in 1796. The designer was again Robert Scot who used art by Gilbert Stuart for the design. He designed them with edge lettering of ‘FIFTY CENTS OR A HALF DOLLAR’ with decorations between the words. For the dollar, the edge had the lettering ‘HUNDRED CENTS ONE DOLLAR OR UNIT’ with decorations between the words. The Draped Bust coins had two reverses; the small eagle and the heraldic eagle. Both had similar edge lettering.
Capped Bust Half Dollar
The Capped Bust Half Dollar was designed by John Reich, the Second Engraver in the U.S. mint, and minted between 1807 and 1836. These coins had edge lettering with the words ‘FIFTY CENTS OR HALF A DOLLAR’. From 1814 to 1831, it had a star added between FIFTY and DOLLAR. From 1832 to 1836, vertical lines were added between the words. After 1836, the Capped Bust Half dollars stopped having edge lettering and had reeded edges instead.
Modern edge lettering coins
Presidential dollar coins
Presidential dollar coins have been minted from 2007 with edge lettering. For the 1st two years, ‘IN GOD WE TRUST’ was included in the edge. The edge lettering also included the date, mintmark, and ‘E PLURIBUS UNUM’. A dot separated the ‘E PLURIBUS UNUM’ and ‘IN GOD WE TRUST’ in the 2007 coins. In 2008 coins, an extra dot demarcated the date/mintmark and ‘E PLURIBUS UNUM’. 
In 2009, when there was a public outcry after most mistook that the coin was missing ‘IN GOD WE TRUST’, it was removed from the edge and added in the obverse. Instead of dots as delimiters, stars were used between date/mintmark and ‘E PLURIBUS UNUM’. The common error with the Presidential coins was some coins completely missed the edge lettering and had smooth edges instead.
Native American dollars
The Native American dollars are another Modern American coins that sport edge lettering and have been minted from the year 2009. The obverse has the design of Sacagawea and her son Pompey, designed by Glenna Goodacre, the sculptor-artist and the reverse changes every year. These coins have edge lettering just like the Presidential $1 coins featuring the date, mint mark and 'E PLURIBUS UNUM' separated by stars.
30th Anniversary Proof American Silver Eagles
The American Silver Eagle coins were first released in the year 1986. For it's 30th Anniversary this year, the U.S. mint is commemorating the coin by releasing the Proof Silver Eagles with edge lettering. The coin has a smooth edge with '30th ANNIVERSARY' incused in italics. The bullion version that was released earlier this year had the traditional reeded edge. After it's release in September, this Proof version has been much in demand with collectors.