Briefly looked into this just out of curiosity. From what I gather you send your track off to PRS and they encode the high frequency watermark over the top for you and send it back, so it can be spotted quickly for royalties.

But tbh, I can't see PRS giving anyone royalties but the big labels and they've also been serious cnuts taking people to court who've only played music they've got consent directly from non-PRS signed artists.

Basically unless you're a big label, you're not going to have the capital to take anyone to court even with definite proof that the track has been bootlegged.