The tear on Julia Dahl's back just looks like a tear. I suppose with a certain mindset, though, it can look like the Japanese hiragana symbol そ (so). According to a
kanji lookup, the glyph most commonly associated with that pronunciation is
祖, which means "founder" or "ancestor".
But to be honest, I think that we're starting to find things that aren't there. A lot of this stuff is fun to theorize about, but I'm pretty sure that we've crossed into territory that FG didn't even really think about. Either that, or they are the world's greatest secret keepers, even going so far as to implant a bunch of obscure Punic War references and Chinese/Japanese characters building up to a huge reveal, and then all but abandoned that game in order to move onto future titles without even a *winkwink* indication that there was something to find.
While I am convinced that this whole Carthage thing has merit, I don't think that it's a great buried secret so much as a subplot that FG intended but never really fleshed out, or had to cut for time or content reasons.