I wouldn't desecrate a shahada for the sake of desecrating a shahada. But if a flag contained a shahada (for example Saudi Arabia), would it be forbidden by Islam to desecrate that flag?
You inquired about a nice inquiry. Yeah, seemingly it has the ruling of Allah names (and his Rasul (Apostle)), then it could be compared with desecrate a paper which consists of Allah names. consequently we ought not to desecrate it even if we do not its country or brand.