I have not. In my attempts to understand the magic of this world, I have never yet come across any other example of such a thing, personally or in writing.

[So... where could this magic have come from? He couldn't begin to guess.]

The magic of my home, of course, was not aligned to Zenith or Meridian either. Perhaps the lack of such signatures is related to the portals' connection with other realities. Or perhaps not. Either way, it certainly suggests something strange about their provenance.