"Residents only" parking sign

[BHML]

There is a road near my son's school which is a cul-de-sac and it has "residents only parking" sign at the road entrance. There are a number of marked bays, but no additional signage (other than the main sign at the road entrance). There are also no resident parking permits, etc in operation. Anyone can park there during school pick up times and whilst there are traffic wardens on the main road, I have never known of anyone being fined for parking in the cul-de-sac. But as you might imagine it has led to some unpleasant exchanges between residents and parents dropping off/picking up their kids from school.

From a legal perspective is the "residents only parking" legally enforceable?

[BHML]

JQ said:

Is it possible it's a private road?

The sign just says residents only parking - there is no signs alluding to it being a private road...

[BHML]

Just talked with the council responsible for this road. Apart from small pockets of land near the garages, the remainder of the road is adopted and under no parking management system. So provided people park within the marked bays, it is legal to park there. They said it's no different to someone parking on the road outside your house.