Double negative reminds me of the following sign commonly found on Missouri's back roads:

"No passing zones unmarked"

In a similar vein I have yet to find a "Dead End" sign anywhere near the entrance to the road so noted, usually its about a half mile into the road.

and "Road not thru" is another common Missouri sign.

"Men in Trees" is an actual road sign, not just a funny sitcom.

CB

"Bear Left"