Edenic

So the Lord scattered them from thence upon all the earth, and they left off to build the city.
Therefore the name of it was called Babel, because the Lord did there confound the language of all the earth: from thence then did the Lord scatter them upon all the earth. Genesis 11:8-9

A constructed (or re-constructed, depending on who you ask) alphabet¹ used in Galicia - claimed as an Adamic language. While the basic use of the script is not secret, it’s said to hold mystical additional teachings that adherents must find or be taught.

It is not common even in Galicia - almost always related to its mystical significance - and even less so in Britain proper.

Footnotes

1. The script I’m using for this is Heinrich Cornelius’ Agrippa’s Malachim. Obviously this was created far from the time period of the game, but with a similar purpose - one of several similar scripts in the later medieval/early-modern period. ↩