With the American economy thriving at the turn of the century and coin operated machines being made in large quantities, Indian Head cents were needed in record numbers. Production increased as they entered the "common date" and final phase of their lifespan. 1907 had the highest mintage and is the only date to top the 100 million mark (108,138,618).
The exception to these large mintage numbers, and the two coins from this period that are excluded from the common date grouping, are the 1908 & 1909 San Francisco Mint coins. These Indians featured a small S mintmark on the reverse below the wreath. They're the only two issues of the series not produced at the Philadelphia Mint.
A total of 1,115,000 1908-S coins were minted, and the 1909-S production of 309,000 pieces is the lowest business strike of the entire series. They're more available than their mintage figures indicate due to increased awareness of numismatics and the knowledge that these were the last dates of the series.
Planchets for both these San Fransisco issues usually have light straw colored or yellow streaks, sometimes subtle, sometimes giving a pronounced woodgrain toning effect. The same planchet characteristics are seen on the 1909-S V.D.B Lincoln.