Not just a prank. This is evil.

I don't know of any backstory, though it appears to have been photographed outside the U.S.  Perhaps a reader with Facebook access can check the original source re details.  Via Just a Car Guy.

Addendum:  I can always rely on my readers.  Within a couple hours an anonymous reader found the original report at the BBC.  The incident occurred in April of this year on the A9 in Inverness.