Since August 2009 those in receipt of planning permission for certain kinds of development will be required to complete and display a Site Notice in a prominent place at or near the site of the development permitted and where it is readily visible to the public. This is a legal requirement.
The categories of permission concerned are for national and major categories of development and for "bad neighbour" developments (e.g. licensed premises, restaurants, hot food shops, development over 20 metres in height and other categories of use specified in the Regulations).