In case you missed it: In a recent video from FOX it was confirmed that the mysterious writing used by the Observers does not derive from the language of an ancient civilization.
Contrary to some fans theories, particularly those from the first season, the language was actually made up by Michael Cerveris, who plays everyone’s favorite Observer, September.
Fringe prop master Robert K. Smith explains the origins of the Observer language:
“[Michael Cerveris] used this notebook in the diner in [The Arrival]. From his notes in the book we extrapolated and made a language, now there’s actually a font you can get, we call it The Observer.”
Cerveris has himself spoken about the amount of say he had in building September’s character, which in turn set the template for the Observers in general.