Oh look, it's a dain.

[Helmut Winkler]

I suppose it is no use but for the record

1) dain is d' aui with an abbr. stroke and means dicit auicenna and in my opinion a key to the whole thing

2) the 'unknown writing system' IS a late medieval script,  I would say a Gothic cursive or a  Bastarda consisting more or less of abbreviations