Hi
We have cctv both around our property and in car cctv (front and rear)
We do not display any signage and my experience is those who put signs up, mostly do not have proper cameras, and most bad people easily recognize dummy from real cameras, so signage I think does nothing
A point though if you do have cctv, particularly if it covers road side, the police may call to ask to review footage if they are trying to trace an event that may have happened but not directly involving your property.
Lastly, most bad people intent on breaking into your property, would have already determined if your cctv is real or fake, even if you do not display signs, and will cover their faces but also attempt to find the recorder, to take with them
Many thanks
John