Surely, for 'no sleeping', they have to prove you're in there anyway. If they knock and you don't reply, they can't just assume you're sleeping. If they knock and you DO reply... then you're CLEARLY not sleeping! In the summer, I parked one night on the seafront at Southwold, of all places. Prime position, in a town where I was later informed they routinely round up motorhomers and send them to the gulag. I parked up at 8, then went into town, returning at about 10. I then went straight to bed. In the morning, I had a shower and breakfast, and was on the move again by 10. It was only when I drove away that I saw the 'no overnight camping' sign on a nearby lamp post. I got away with it. But what would anyone have had to complain about during my stay? Nothing. Supposing I'd been visiting friends on the seafront and had stayed in their place instead of the van, and the van was just parked there. Surely, what I said earlier applies. If they knock and there's no answer, they can't just assume.
I tend to park somewhere neutrally to do my cooking. I then quite often leave it until late in the evening/after dark to drive to where I'm going to stop over, then go straight to bed.
'No sleeping or cooking' is, to my mind, just code for 'no campers or motorhomes'... so why don't they bloody say that?
As for 'no camping'... wtf does that mean, anyway? I'm not pitching a tent, and I don't have a caravan taking up an extra space. I have a small motorhome, which I might choose to kip in as I would a car. Is that 'camping'?