Decided to take a look at my SBA's and found 2 "S" M/Ms in there too. Weren't they proof only? These don't look it.
Circulation strike coins were made in San Francisco in 1979. They are as common as the P or D mint coins.
Here is some info on type.http://www.varietyvista.com/14 SBA Dollars/San Francisco Mintmark Styles.htm