Or we might have to wait until we get more info in the books
Well yes, but that's like finding out who lives in the white house third from the end with what kind of pet and what they do by knocking on the door and taking a census. No fun at all.
It's always possible that I'm right about the prehistory, and that it's from a time when humans had writing, or at least pictographs for recording information/warnings, and that they were
still put there by some non-human entity.
Another question though, if the runes are prehistoric, that means the Lighthouse is prehistoric. So who made that? The earliest recorded evidence of a light house is the Pharos, but even that was only built in 300 BC (or so). We'd be looking at something probably 2-3 millenia older than that if it's prehistoric.