For a negotiation, I went to the offices of a respected law firm in an upscale Paris neighborhood. (The negotiation went well, thank you.) At the end of a productive morning, before heading out into icy Paris streets, I asked if I might use the bathroom, to which I was cheerfully escorted. After heeding the call of nature, my eyes lit on a paper –not a poster, but a sheet of office paper– affixed on the bathroom's inside door. The paper said, in essence but in folksier terms, "Think of those who will be next. Please leave this place as clean as it was when you came here," and featured a clipart sketch of a gleaming toilet.

I mean the point in a joking way, but the firm's reputation took a dive after I saw that.

This is a firm where the managing partner can take time –his own and his secretary's– to produce a notice. But the managing partner lacks the courage to put these words into a memo, to be circulated throughout the office. And he lacks the authority to say, at an office meeting, "We owe it, to ourselves and to our clients, to keep the office bathrooms spotless, and I ask you all to take special care to live up to this expectation."

There's an alternative explanation (still put forward in a joking way): the firm is cheap or indecisive when it comes to housekeeping. Perhaps more than weekly/biweekly/daily janitorial service is needed. There's a tradition in French cafés and train stations, of a bathroom staffed by a Dame Pipi, whose job is to maintain the premises in pristine condition, and who assesses a few coins from each user.

A reader obliquely suggested another way out of this predicament: give a nudge. This is the title of Richard Thaler and Cass Sunstein's book, which discusses ways to draw attention and influence behavior in a positive way, but without dictating anything. There was an interesting experiment carried out in the men's room at the Schipol airport in Amsterdam: flies were painted onto the urinals. The surprising effect: "spillage" onto the floor fell by 80%. Thaler surmises, "Men evidently like to aim at targets."