"It was only when placing one of the beams aside we happened to put it down with daylight glancing along its length and we spotted that it . . . was covered in apotropaic markings."

BB:

A customer came in one weekend looking for “an oak beam for his fireplace lintel.”

...

Apotropaic markings, or protection marks, are basically magic symbols thought to ward off evil influences and keep malevolent fates at bay