FCGetMetricSignature[] returns the signature of the Minkowski metric used when working with Cartesian objects, such as CartesianPair, CartesianIndex, CartesianMomentum etc.
{1,-1} corresponds to (1,-1,-1,-1) and {-1,1} means (-1, 1, 1, 1).
Overview, FCSetMetricSignature.
FCGetMetricSignature[]\{1,-1\}