Ha-ha wall
When I read "Ha ha Wall" and saw the picture, I instantly assumed that it meant the people on the "safe" side of the wall could tease/taunt the people on the "difficult" side of the wall - like Nelson in the Simpsons, "Ha ha!"Guess I was wrong.  Maybe less than 100% convinced I'm wrong, but I probably just fell in love with my own explanation & I'm unwilling to fully concede.