You have a stamp with a small portion of a registry cancel on it, similar to the cover here:

During the period that your stamp was current, the registry rate was 8 cents until October 31, 1908 (plus the 2 cent letter rate), and then 10 cents beginning on November 1, 1909 (again, plus the 2 cent letter rate). So your 10 cent stamp was very useful on registered letters.