Assigning a role based on signup url on a Drupal 7 site?
You can do it with Auto Assign Role module, It provide paths that will trigger a specific role when an account is created.


  The Auto Assign Role serves three primary purposes. The first is to
  provide an automatic assignment of roles when a new account is
  created. The second is to allow the end user the option of choosing
  their own role or roles when they create their account. The third is
  to provide paths that will trigger a specific role when an account is
  created. The administrator has full control over these functions and
  can have them working together or independently of each other. Auto
  Assign Role is integrated with the Content Profile module so that you
  can have content types serving as registration pages. You can even
  replace the default user/register page with a customized version of
  your own design.