I once worked at a factory where i was the only white and you simply could not leave anything in the break room fridge.
They were pretty sophisticated about stealing each other's lunches, using lookouts and staggered break times, and being white I couldn't depend on anyone for info or watching. There was no "nice" way to deal with it.
Hypodermic and ipecac to the rescue. You only use *a little*, or else someone is gonna be calling an ambulance and get you charged.
DO NOT put the bait in your own lunch, it has to be something different, for legal reasons. microwave burrito, prints wiped, furtively tossed in a back corner, is a good choice, and barely touch a cigarette lighter's flame to the hole afterward so if the thief is smart enough to squeeze the package for air-proofness, he'll be fooled. Probably an unnecessary step when dealing with niggers, but you don't want them to know they got dosed.
Anyway, see who pukes his guts out. You can't brag but at least you'll know. Cools it off temporarily.
A kinder, gentler, solution that I saw used by a guy in a large rooming house: Label containers with name of whatever body fluid most closely resembles the contents. Egg-drop soup is "pus", couple drops of tobasco makes it "bloody pus". Use your imagination.
No time for the old in 'n out, love. I've just come to read the meter.