Handle with care
Just like "Fragile" or "This side up", this labeling will almost 100% guarantee that your parcel will be tossed, bounced, drop-kicked, and/or stomped upon by disgruntled/delinquent shipping-personnel during its entire journey from you to your intended recipient. Yep, I'm talking to YOU, USPS/UPS/FedEx!!! There --- I said it --- got it off my chest! :P
During the infamous "angry political activists shooting at passing semi-trucks" period back in the 80's, some truckers apparently resorted to painting their trailers with huge "Caution: explosives"-type signs to discourage nearby riflemen who would prefer not to get blown up themselves along with their intended targets. A cartoon in a magazine during that time showed two redneck 18-wheeler-drivers discussing a huge "WHAMMO DYNAMITE" label that the speaker has painted on the side of his van; the driver is saying something like, "Actually, I'm hauling dried prunes, but I feel a lot safer this way, rather than my having 'Handle with care' written on there instead."