Naming and Shaming
When the repeat offender (or food borrower) is known to the kitchen users, the victims will often find ways to retaliate that may protect the fridge contents. Either way this is less than subtle way of letting everyone know just who is the food pilferer. This naming and shaming method could backfire of course, leaving the field open for the people not named and shamed to take advantage of the situation, take the food,and lay the blame firmly on the wrong person.
In the pic shown it is obvious that all of the staff have a good idea who is taking the food!
Debbie has nowhere to hide in this case.