Remember that your location is vital here. I'm assuming UK law:
https://www.gov.uk/government/publications/domestic-cctv-using-cctv-systems-on-your-property/domestic-cctv-using-cctv-systems-on-your-property
You'll find this section:
"3.3 Letting people know about your CCTV system
Ensure that you are transparent to those around you when installing your CCTV system. You can do this by:
- informing your neighbour(s) about your system
- putting up a notice informing people that recording is taking place"
Equally if you were to use recordings as evidence in a dispute, you will no doubt end up capturing video of areas that are beyond your land ownership, and not being transparent that you have CCTV in operation could cause all sorts of legal disputes in this way.
So is it an absolute requirement? - Not necessarily (but I'm not 100%).
Is it best practice / recommended? - Absolutely.
A take on the official guidelines state this:
"3.3.1 People in public places should normally be made aware whenever they are being monitored
by a surveillance camera system, who is undertaking the activity and the purpose for which
that information is to be used. This is an integral part of overt surveillance and is already a
legal obligation under the 1998 Act. Furthermore, such awareness on the part of the public
supports and informs the concept of surveillance by consent. "
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/282774/SurveillanceCameraCodePractice.pdf