And now for another edition of Signs & Seals:
This is a symbol referred to as the "Twin Triangles." It is a symbol that represents or accompanies the Archangel.
The symbol sort of looks like two hourglasses, which might represent Death's Hourglass, death leading to the Archangel. Or not. The symbol isn't really clear and nobody really has explained what it has to do with the Archangel. In this respect, it is similar to the Operator Symbol.