Besides having the proper electrical schematic forr your car, only way to be sure is to take a measurement with a voltmeter.
Turn the ignition on then look for 12V on one of the wires. If you don't have voltmeter, you can simply connect up a tail light bulb. The other wire from the bulb should be connected to ground (negative).
I'm not sure it would be 12V. These wires come from the distributor and I am pretty sure carry only the magnetic signal generated by the stator/reluctor. I have the FSM but it doesn't refer to polarity. I am hooking up an MSD6A and the wires are violet + and green -. The wires from the distributor are red and green. Again intuitively, you would think red is +. I think they carry only a low voltage pulse signal.
I think what Sizzler is getting at, is that DC circuits always have a hot and ground, typically red and black, vs AC which have hot, neutral, and ground, where typically green is ground and black is hot. Obviously cars are always DC.