Excerpt compliments and courtesy of Lincolncentresource.com. Copy and Pasted:
San Fransisco Mintmark Styles
Mintmarks have changed design many times during the
Lincoln Cent Series. The San Fransisco
Mintmark "S" has actually changed 15 times!
Here is a list of all the San Fransisco mintmark styles:
Mintmark Style-001 (Blocked Serifs) used from 1909-1916
Mintmark Style-002 (Small S) used from 1917-1941
Mintmark Style-003 (Large S) used only in 1928
Mintmark Style-004 (Trumpet Tail Serifs) used from 1941-1942 and again in 1945-1952
Mintmark Style-005 (Straight Serifs) used from 1943-1944
Mintmark Style-006 (Ball Serif) used from 1944-1946
Mintmark Style-007 (Sans Serif) used from 1946-1947
Mintmark Style-008 (Tall S) used from 1952-1974
Mintmark Style-009 (Blob S) used from 1974-1979 (74 proof & business strikes, proof only 75-79)
Mintmark Style-010 used from 1979-1981(proofs only)
Mintmark Style-011 used only in 1981(proofs only)
Mintmark Style-012 used from 1982-1984 (proofs only)
Mintmark Style-013 used from 1985-1989 (proofs only)
Mintmark Style-014 used from 1990-1999 (proofs only)
Mintmark Style-015 used from 2000-2007 (proofs only)
Mintmark Style-016 used from 2008- Pres (proofs only)
Mint Mark Style-009

This mint mark style was used from 1974 to 1979. Hope this helps.
