Evolutionary biologist and graphic-design geek Colin Purrington (author of the fantastic taxonomy of lab-notebook inks) has an issue with bathrooms. Specifically, with bathrooms so badly designed that no one washes and dries their hands adequately, and then everyone is forced to touch a door handle in order to exit. He’s sufficiently exasperated that he not only blogged his annoyance, he came up with some public-health messaging to share the spleen: a set of signs formatted for printing onto large-scale Post-It sheets, suitable for guerrilla adornment of any door or a hot-air blower.

My pet...