SMS means "Special Mint Set"
This designation is used for coins that were distributed only in mint or commemorative sets by the US mint but are otherwise similar to the regular buisness strike coins. Most mint sets contain "Business Strike" coins that are exactly the same as the coins that go th the banks to be used in everyday commerce. SMS coins are ony made for distribution to collectors in sets sold by the mint and are Special in some fashion.
They can be found for the years 1965, 1966 adn 1967 and include the Lincoln Penny, Jefferson Nickel, Roosevelt Dime, Washington Quarter and Kennedy Half Dollar. The half-dollar is of clad composition and contains 40% silver, the same as the business strike coins of those years. During these 3 years the mint suspended proof coin production but due to the demand from collectors they made the SMS coins instead, which are made in slower coin presses using polished dies to give a superior finish. They are not up to the standards of proof coins of other years yet are better quality than the business strike coins. SMS coins can also be found with a Cameo finish on them, much like the Cameo finish on a proof coin. This is due to the additional care used in striking the SMS coins. And like Cameo proof coins, Cameo SMS coins command a higher price. You will find many of these coins being sold as singles and many of the coin albums avaliable have a slot for both the regular business strike and the SMS coins.
In 2005 the mint started producing satin finish coins that are only available in mint sets. These are also SMS coins. Up to that point they used business strike coins to make up the mint sets. This makes 2 distinctly different coins in the P and D mint marked coins as the satin coins are made by superior processes and have the satin finish. As of this time I have not seen that the album companies are adding slots for these SMS coins but it will come due to collector demand. A fully complete set will contain the P mint business strike and P mint satin SMS coins and the same for the D mint coins.
There are a few other SMS coins that have been minted thorough the years. In 1994 there was a matte finish Jefferson nickel that comes in the 1993 Thomas Jefferson 250th anniversary commemorative set and then another Jefferson nickel in 1997 again with a matte finish and issued in the Botanic Garden commemorative set of the same year, both of these coins bear the P mint mark.
1998 s matte finish silver Kennedy half dollar is another SMS coin that was issued in the Robert F and John F Kennedy commemorative set of that year. There may be others but these are the ones I am familiar with.
Many have asked me about these coins and I do hope you find this guide helpful.