I live in an area of densely packed Victorian terraces and there are always a lot of estate agency boards. Some of them are left up for a very long time, and just say things like "Success" and "Similar Properties Required" rather than "Sold" or "Let". In Summer there are also a lot of agency-sponsored boards going up to advertise school fetes and other charity events (the agent donates a few hundred pound to the cause if a minimum number of people agree to put a board up for a few weeks).
I've been looking at the Town and Country Planning (control of advertisement) Regulations 2007 here: www.legislation.gov.uk/uksi/2007/783/made.
The regulations state that: "No advertisement may be displayed indicating that land or premises have been sold or let, other than by the addition to an existing advertisement of a statement that a sale or letting has been agreed, or that the land or premises have been sold or let, subject to contract". Does that mean it is illegal to simply display the statement "Success" without any information about the transaction that has taken place? And is there anything in there to control the proliferation of sponsored boards?
The same regulations also say agency boards must be removed within 14 days of completion of a sale or the grant of a tenancy, but presumably this relies on people actually complaining and asking for them to be removed.