Seeds of Evil
See also Occult Symbols
The strange symbols seem to have different meanings. They seem to have power associated with them, including marking someone as a beacon, perhaps heralding the arrival of something as well as appearing randomly on phones, rending them useless.
It was revealed, upon reviewing the text, Piercing the Darkness that this was a language, developed by the Tannhauser Bruderschaft resulting from contact they had with the Outer Black as a way of casting powerful spells and rituals.