Most effective was this sign I saw on terrariums containing alligators inside a bar:
Alligators have survived since the age of dinosaurs by preying on the slow and the stupid. Do not put your hands in the tanks!
LOL, while there is nothing funny about this poor kid, there is something funny about watching a bunch of wildebeests walking down to the water to drink.
The entire herd looks nervous and holds back, shuffling from hoof to hoof, and one dimwit walks up to take a drink and is dragged in by the nose. The others see this, and now go down to drink!
When I was in the Navy, I was working on the flight deck, and me and one of my squadron mates were standing there, side by side with three heavy tie-down chains draped over each shoulder, trying to figure out if we were too close to walk in back of an F-14 Tomcat that was waiting to launch. We nervously looked at each other, but neither of us walked in back of the idling jet engines.
Then, a Blue Shirt carrying a pair of chocks in each hand, walked up next to us, paused for a split second trying to determine if it was safe, and after about 1/10th of a second of internal debate, stepped out into the jet exhaust.
He got blown down the flight deck, legs, arms, and chocks in a big tangle.
We looked at each other, nodded, and took the long way around.