I had a different idea, but it does not quite fit into Mur's definition of a counter-symbol.
Here's a shape which, when added to Mur's symbol, completely messes up its meaning.
It makes the symbol of whatever it was into a symbol of reflection, thus destroying the meaning of the original symbol )
[img]http://lh5.ggpht.com/_y4aqSnXq6kA/TQP0M1QCLXI/AAAAAAAAABY/Qx0ChIv_RZo/recruit.jpg[/img]