Disambiguating names according to scopes in C++

Consider

int biff;
int var;
struct Var {
  int var;
  void foo(int var) {
      biff = var; 
  }
};

Which var is used in the assignment? Sure, a good C++ programmer knows the rules. But it can be hard to tell in a large program. You can disambiguate for the member

      biff = this->var; 

or the global

      biff = ::var; 

But so far as I know there is no syntax for arguments. I often use a naming convention

  void foo(int arg_var) {
      this->var = arg_var; 
  }

This is not unlike the widespread convention of saying

  void foo(int arg_var) {
      m_var = arg_var; 
  }

although I deprecate this because m_var for member names can lie - there may be a global of that name. Whereas this-> is not much bigger, and has the compiler check your meaning. Perhaps there should be sigils, like this-> and ::, for arguments and locals? -- Late addition, 5/25/2012: I dislike extra typing. Plus, occasionally I will do a refactoring where an arg or a global becomes a local or a member. Sometimes I want such refactorfings to show up in history diffs, sometimes not. Here's an interesting possibility: have the build or ODE system annotate the code with a hidden sigil (which I would suggest being XML, something like . Have the IDE warn if an edit would change the implicit sigil. Much as GCC warns if an inner scope hides an outer scope's name.