It might not quite be a banksy, but the council dog stencil does seem to be fairly effective at keeping the hill clean and safe, at least in the bits it appears; I certainly would tread carefully walking across the roundabout lawns on the wimpey estate, or certain parts of eaglesfield or shrewsbury park or the woods, although things are getting better.
Anyway it seems to be a fairly serious initiative with its own enforcement officials being geared up to hit anti-social dog-owners where it hurts, i.e. the purse.
I’m not sure what kind of dog the stencilhound is? I once saw a similar street painting in paris, and it was definitely a lapdog of some sort, you know the type that fits in a handbag, but the Greenwich version appears to be modelled on a cross between a Poodle and an Alsation, I call it a Poosation.