So I uploaded this a week ago, and people say that it means Xûr is in the Tower, which I guess is true, because it disappeared on Sunday.
But this week, I checked the symbol again. It was DIFFERENT! The number above the triangle was XI, instead of X. And the triangle had a different shape inside it, too! What could this be?!
EDIT: Someone necrobumped me. I know what it means now. It shows that Xûr is in the tower, and the Roman numerals could be referring to his location.