Part of the ethos of a lean organization is the constantly improve by exposing problems and then systematically solving these problem. Visual controls make problems visible by providing norms you can see. The best visual controls are simple, unambiguous and direct. I saw this visual control on the window of a Budapest subway recently. It is what I would call an ambiguous visual control.

At first glance you can mistake it for the familiar "do not" symbol of the red circle with a line through it. However, closer examination only serves to befuddle.

What could this possibly mean? Perhaps "it is OK to rest against the window?" It almost looks like this stick figure person is taking a seat on the window sill, all of 1 cm wide. But why would anyone want to spend money printing and adhering labels to indicate this?

The Budapest subway stations are rustic and charming with old tile and woodwork, so could the sticker mean "come and peer out the window?" Since the window was open, the meaning may have been "these windows can be opened" but this is also odd since the windows do not open from bottom up but pull top-down. These sorts of visual controls could almost make us feel we are not following some simple instructions that everyone else understands.

This doctored version of the visual control is clearly saying "whatever you're thinking about doing to this window, don't do it!" and only true rebels would approach the subway window with bad intent. Even if the consequences of sitting / resting against / peering out the window are not clear, people will generally not loiter around windows with such a visual control.

Ambiguity and creates variation and variation creates waste. What's a visual way of saying "post no ambiguous visual controls"?