The 1916-D Mercury dime is one of the most heralded key dates of 20th century numismatics. If you collected coins in the 1950s or 1960s, you dreamed of finding a 1916-D dime...or a 1909-S VDB or 1914-D Lincoln cent, or 1932-D or 1932-S quarter...in circualtion. And I certainly did have that dream as a young pre-teen coin collector.
The 1916-D is rare in all grades. Walter Breen has written that mint production of dimes in Denver in 1916 was stopped so that personnel could devote full time to making quarters. The original mintage of 264,000 for the 1916-D is by far the lowest of the Mercury dime series. For comparision, the mintage of the 1916 was 22,180,080 and the mintage for the 1916-S was 10,450,000. The 1916-D is an extremely high demand coin in all grades and even very low grade examples sell for in excess of $1,000.
The 1916-D is rare in mint state and very rare in Gem condition. The strike is usually very sharp and I'd estimated that 80% of more of the mint state survivors have fully struck crossbands. Luster is typically modest. Many examples have some degree of toning.
Note that this is one of the most counterfeited of all U.S. rare coins. The bad guys add a "D" to a 1916 Philadelphia. I have seen counterfeits in all grades and PCGS sees an average of 5 to 10 counterfeits a week. Needless to say, third party authentication is highly recommended.