A label saying "This container is for coffee _ _ _ _ s" with a lettered padlock (http://wordlock.com/padlocks/ http://wordlock.com/padlocks/) would perhaps be p

A label saying "This container is for coffee _ _ _ _ s" with a lettered padlock (http://wordlock.com/padlocks/ http://wordlock.com/padlocks/) would perhaps be preferable to the hidden key solution.