Personally IMO all pathetic displays of religious beliefs should be banned in such situations.
But just looked up this "shadada" and it is descrided as a symbol of faith so it is no different to a skull cap, silly braiding, turbans or any other symbol.
It the meaning of it may very well be distorted when used by suicide bombers and the like - just as the religion it self is distorted but that does not change it's true meaning.
