EtaSign is an option for SFAD,
GFAD, CFAD and other objects representing
propagators. It specifies the default sign of the i \eta prescription in the propagators,
e.g. for standard Feynman propagators the value 1
corresponds to \frac{1}{p^2-m^2 + i
\eta}, while the value -1 sets \frac{1}{p^2-m^2 - i \eta}.
Notice that if the sign of i \eta is already specified in the propagator, e.g.
CFAD[{q, {m^2, 1}}]\frac{1}{(q^2+m^2+i \eta )}
then this specification always overrides the EtaSign option. Hence
CFAD[{q, {m^2, 1}}, EtaSign -> -1]\frac{1}{(q^2+m^2+i \eta )}
still has the positive i \eta.