William Vallicella, the Maverick Philosopher, discusses
positive and negative signs designed to keep trespassers out. One could make a good no trespassing sign out of a passage of rustic dialect from Shakespeare's
King Lear (4.6.266-268):
Keep out, che vore ye, or Ise try whether your costard or my ballow be the harder.
In my modern English version:
Keep out, I warn you, or I'll test which is harder, your head or my baseball bat.