Don't do that.

One of Lileks' commenters noted that the circle with the slash through it (Don't do it -- be a ghost, smoke, park here) is called a bar sinister or bar dexter, depending on which way the slash goes. It's a (an?) heraldic symbol. So I did what I do: looked for proof.

I found this interesting explanation on Google Answers, although I was immediately put off by the writer's "In amerika, however, ..." There's a trust factor right there.

Here's a compilation of European traffic signs. Remember when it was time-consuming to locate information like this?