...in such a way that no reasonable authority could question them. I think the second label attached to whatever container would do the job.
I should have said: limit the quantities (as has been mentioned) and have them labeled.
If you've got a couple sample packs of Vicodins... meh. You've got a handful of Vicodins w/ paperwork... I would think this would be fine with just about anyone. You've got a bottle of 50 w/ no paperwork... I'd rather not find out the hard way who this may concern.