Simon,
I think its just the sense that leaving a country cousin to lock up on his way out we might return to see an upstairs bathroom fan light window still open and expect the worst. Living in SE London that's "an invitation".
One might walk past a bike and instead of a comment as to how it has an ugly straight front fork or a novel routing of the gear lever cable one might say "call that a lock?"
Touch wood and fingers crossed and all else I've never had any problems in 25 years "south of the river", but one takes precautions as a matter of habit.
Driving past the maisonette in Earlesfield where we used to live we pointed out where you would only park if desperate as with no overlooking property it was about a 1 in 5 your car would be broken into. "Broken in two?" said the kids, that's the problem I have NOW... Parked somewhere like that I'd NOT lock the car as if to say "come in, have a look about, nothing to see" and in the hope that they'd do just that and not smash a window.
So - parked up - battery isolator and a fuel pump switch. If its laid up rotor arm out, ideally battery out, better still on blocks.
Its just the same as crossing the road or anything else. Understand the risks and keep to the rules. Where I grew up in a Fenland village security was, and still is, an even greater problem than here. Go away for the weekend and chances are your roof has been stolen, or your hedge. "Escape to the country" - no thank you very much... At least not that bit
David