"Passion Play" has a totally different meaning--not consistent with the song and likely yet another folk tradition/mondegreen that got passed on.

As I said above, Dick Gaughan sang it as "pledge" and I know of his high standard and committment to tradition, so I trust his research. He stated on the lyric sheet that it was a poem by Patrick Kavanaugh.

But there is another line in that song that I've heard a couple of different ways. It's the "true gods of sound and.." line. I've heard it as "sound and stone" or "sound and time". Now "time" is a near-rhyme to "sign" in the line above...