public String getAvatarIdentifier() returns the unique identifier
      for an avatar rendition.
    Parameters
None
Returns
Returns a String representing the unique identifier for the avatar rendition.
Example
    PersonService ps = session.getServiceRegistry().getPersonService();
    
    Person p = ps.getPerson("joeuser");
    
    Log.d(TAG, "avatarIdentifier: " + p.getAvatarIdentifier());
    Log.d(TAG, "firstName: " + p.getFirstName());
    Log.d(TAG, "fullName: " + p.getFullName());
    Log.d(TAG, "identifier: " + p.getIdentifier());
    Log.d(TAG, "lastName: " + p.getLastName());
      
      Would produce output such as the following: