A couple of these signs have been placed on retail outlets in the Bentalls centre in Kingston, south-west London.
There are two ways of reading them.
The first is that units are ceasing to trade for health and safety reasons. An outbreak of Ebola, perhaps? Or liquid asbestos dripping from the ceiling.
The second is that the posting of mail contravenes health and safety regulations. Although this seems the more likely of the two explanations, I find myself at a loss when it comes to suggesting the potential danger. All ideas welcome via the comment button.