[CamperBob2]

Hmm, I don't know about that. The data rate used by civilian GPS (L1 C/A) is only 50 bps. The symbols are normally spread over a couple MHz of bandwidth to make it possible to recover at levels below the thermal noise floor. I see no reason why the same thing couldn't be done at baseband, adding an imperceptible bit of extra noise to an audio signal.

Of course, you wouldn't encode real-time navigation data, but a small block of identifying text. Either way, though, someone without a copy of the spreading code isn't going to notice it or decode it. Given enough redundancy in both the time and frequency domains, removing it wouldn't be easy either.

[BHSPitMonkey]

The real problem is that bad actors would simply encode some other person's coordinates/metadata into the recordings they produce, and we'll have been trained by then to blindly accept the presence of these markers as strong evidence of guilt.