Really, sydenham central?

There was a spate of it in my part of the world late last year, very rural and lots of travelling types come through in spates.

When I was a boy scout in the 50s we'd use gate markings,but not for thieving.

did you burgle that drum tosh? not me guv.

Utilities use coded colours, blue, yellow, white, purple from those big marker cans for each specific utility. Never do they chalk on gate posts, in fact hey are not allowed to mark on private property such as gate posts, just road surfaces.
They mark the entrance to your house on the pavement if they need to.

Better safe than sorry mrwandle, be vigilant. Never answer the front door and leave the back door unlocked. Never trust anyone claiming to be from some organisation with out checkable ID.

Of course if you subscribe to the mantra " its only a minority" just don't bother.