Trace Wiper

"We are supposed to press the paper with this each time the light flashes," the injured man explains, arranging his paper on a writing board and drawing out a quill without ink. He works through numbing pain, gradually and wheezing away as he moves. "It leaves a dent in the paper. When the light stops flashing and remains steady you leave a space. The pattern of dents and spaces have a meaning attributed to them. It is all keyed there -" he points at a stack of parchment by a side with his injured hand. "You note the message down and then interpret it."