Apparently some people have problems with co-workers stealing their lunches out of the fridge.
So the fine folk here have come up with plastic baggies designed to make it look like your sandwich is moldy.
Which of course means that your co-workers will throw your lunch in the trash. But at least you'll know where it is.
As for me, I like to forget my things in the fridge and get real mold on them. Then I tell my co-workers, "Oh, no, this is not really moldy, it's a fake plastic baggie that makes it appear moldy. Why don't you take it home with you? Oh, yes, I'm sure you'll love it."
I am very popular around the office.