There's a lot of cross-pollination between Jihadist groups over symbolism, even accounting for the fact that they all draw on the same long-standing symbols of Islamic faith in general and (regardless of whether they're Wahhabist or not) of Wahhabi revivalism from the 18th century. ISIS isn't even the only group which uses the Seal of Muhammad on their black flag with Arabic lettering (which I can't read, as a monoglot).