Or, if you have access to the end of the cable in question, you can try to connect it to a pulsed current source (on off on off) and at the start simply check with a tester which one has on off on off..
Similar possibly is it to switch on off load in the end (like having pair of 2k W hair dryers) .. then in the start it's possible to measure the amperes with a Amperemeter or something with volt that should also change a little bit rhythmically?
Indirectly measuring the energy consumption (inductively) :)
Modulation of a signal on top a current, nahhh I don't know. To dangerous. Ask a professional, may be? Make your work be magically someone else' problem hahaha