Or it could be simply an initial--like
Harry S
Truman, whose parents couldn't decide between
Samuel and another S name, so they comprimised by using just S.
Harry usually wrote it "S.", but the birth certificate is without the period.
You can find lots of other initials in those old popularities, like these, which are from the 1900s top 100 list:
J (35th)
W (61st)
C (75th)
A (83rd)
R (92nd)
E (94th)
H (97th)
Miranda