I have a possible theory about the runes themselves. it involves spoilers, so if you haven't finished the game, I say stop reading and finish it!
So as we all know, this is Odin's illusionary rune of camouflage and deception. So I started to ask myself, thinking of the game developers, the storytelling in general, and on all the folklore and myth we've come across. Now we all may be thinking, Odin, probably hid something, or multiple somethings in England. But then I thought, who would Odin want to hide anything from? Why Camoflage, blend in, in plain sight like the titular assassins? And then I had a thought. We all know at this point Basim is the reincarnation of Loki, who currently has all of his old memories, and is currently at the end of the game is the one in the Animus, viewing Eivor's memories. Perhaps Odin, having the gift of foresight, saw that he needed to hide whatever it is from Loki, and the reason all we can see at this time is a symbol of Illusion. Idk, it may be a stretch, but until they release something new about it, maybe this theory can help support another one.