Hi there,
So it’s simple… One its a CT transformer. two depends what it’s measuring / Sensing.
The “+ / –” (P$1, P$2) marks the phase orientation of the winding. You can ignore it if you’re just logging current magnitude, but if you’re doing multi-phase power measurement, direction detection, or power factor, then you need to respect it. Hooking it backwards flips the sign of your current measurement.
HTH
GL 
PJ 
Good question BTW 