I heard a tale, years back, of an area where local farms were frequently trespassed by hunters - despite prominent NO TRESPASSING, NO HUNTING, &c, signs. Anyway, new signs appeared around one farm perimeter: WARNING: RADIATION HAZARD TO UNPROTECTED PERSONNEL!
This had the desired effect ... but the other farmers came around ... worried about "radioactivity" ... and the canny farmer said: "Well, the sign means what it says - any fool walks about without sunscreen ... might get sunburned!"