CSIE[i] can be used as input for D-4-dimensional \sigma ^i with D-4-dimensional Cartesian index i and is transformed into PauliSigma[CartesianIndex[i,D-4],D-4] by FeynCalcInternal.
CSIE[i]\hat{\sigma }^i
CSIE[i, j] - CSIE[j, i]\hat{\sigma }^i.\hat{\sigma }^j-\hat{\sigma }^j.\hat{\sigma }^i
StandardForm[FCI[CSIE[i]]]
(*PauliSigma[CartesianIndex[i, -4 + D], -4 + D]*)CSIE[i, j, k, l]\hat{\sigma }^i.\hat{\sigma }^j.\hat{\sigma }^k.\hat{\sigma }^l
StandardForm[CSIE[i, j, k, l]]
(*CSIE[i] . CSIE[j] . CSIE[k] . CSIE[l]*)