That's te thing: if this technique is as commonplace as they claim it is, in a world where films and television are hurled at us like water from a firehose it shouldn't be hard for them to show examples of such prop and scene marking in other film and TV. Like all other arguments, however, supporting examples seem to be beyond them.

Frankly, I would expect any scene-setter to be hauled over the coals for leaving such obvious markings on any prop or piece of scenery that's supposed to be in shot.

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"The very powerful and the very stupid have one thing in common: They don't alter their views to fit the facts, they alter the facts to fit their views." The Doctor, Doctor Who: The Face of Evil.