Watermelon patch
 

A farmer was having trouble with someone stealing his watermelons, so he decided to fix the problem. He went out in his Water melon patch and posted this sign " Attention" In this watermelon patch is one poison watermelon" signed Farmer Brown. To his delight, no more melons was taken, but then he noticed below his sign a handwritten note was scrawled " Now there are two !"

Deleted due to inappropriate adult content.