Founded in or before 1902...so no: agd, aephi, dphie, sdt, or phi sig.
that still leaves us with:
adpi
azd
aopi
asa
ast
a phi
a chi o
g phi b
dg
tridelt
dz
zeta
theta
kd
kkg
pi phi
sk
sigma
phi mu
chi o
that does not narrow it down a lot! though i think someone mentioned there isn't asa in nc?
i'm thinking it might be zeta because you were so excited about the one zeta's signature or sk or sigma because you pointed them out...
i'm so curious!
my main guess right now is sigma sigma sigma