A 2:
It is impermissible to write anything by any means on the forehead of the dead person. Moreover, it is impermissible to write anything on his grave; this is applicable to shahadah and anything else since it is categorized as Bid`ah (innovation in religion). The prophet (peace be upon him) himself did not allow
writing on the graves of dead people, and this applies to writing on any part of his body because this does not avail him anything.