Since the support definition must be generally valid, the nonlinearity specification always refers to the coordinate system X',Y'Z' of the support.
If you define a support with "Failure if PZ' negative", the support fails if the "acting support force" acts against the axis Z' in relation to the support coordinate system.
If you define a support with "Failure if PZ' positive", the support fails if the "acting support force" acts in the direction of the axis Z' in relation to the support coordinate system.