If you are a homeowner, and the cameras are only fixed on areas within your boundary (for example, a back garden) then you are not legally required to display signage. If, however, the camera captures areas outside of your boundary (for example, the street outside your house) then you should have signage in place.
For businesses, clear and visible signage stating the organisation responsible for the system, your contact details, and the reasons for recording, must be on display. You must also specify if the cameras are recording audio. This signage must be located anywhere where people who can be captured by your cameras can see it.
Note: Businesses using CCTV must also register their details with the Information Commissioner’s Office (ICO) and pay a data protection fee, unless they are exempt. Check to see if your business is exempt here.