The Camden website states, presumably underpinned by its policy, that:
Where you can park with a Blue Badge in Camden
.....
residents or paid-for parking space, if it is not in the Green Badge zone or housing estate.
The traffic sign in evidence is a bog standard Residents parking only sign. Nothing on the sign indicates that the location lies within a 'Green' zone.
How would a motorist know when parking that they were not permitted to do so?
For the purposes of parking, the council has chosen to call the 'exempted area' under the 2000 Local Authority Traffic Orders Exemption regs a 'Green zone'. I don't know how their TMOs deal with traffic signs for parking places in this zone, but it's not overlaid with statute and therefore must be included within orders.
And as regards its display, as I understand it these provisions apply:
Display of an individual’s badge when a vehicle is parked
14.—(1) This regulation prescribes for the purposes of section 21(4A) of the 1970 Act the circumstances in which an individual’s badge may be displayed while a vehicle is parked.
(2) An individual’s badge may be displayed on a vehicle while it is parked if it–
(a)has been driven by the holder, or has been used to carry the holder, to the place where it is parked; or
(b)is to be driven by the holder, or is to be used to carry the holder, from that place. (my emphasis)
OP, my thoughts are to go with what you know and the circumstances and that because there wasn't any indication on the traffic sign, which is shown in their photos as being a standard 'permit holders only' sign, you are still not clear as to why the PCN was issued.