So here's what I got. [may as well start this off with a bang, right???] No idea who or what wrote that sigil, but it's powerful. They think that it's more complex and powerful than the apes had the ability to do, so signs point to the apes having help from one of EssTee's enemies. They were shockingly unforthcoming about which enemies they think it might be--[heaping amounts of sarcasm right now]--but basically it'd have to be something pretty powerful. Which means whatever it's keeping out or in is important. Also, destroying the door will destroy the seal, but I'm super not interested in doing that just yet; not until we figure out more about it.