The Red Room by William le Queux

I stood awaiting his return for a few moments, and then followed him out upon the landing, where my feet fell noiselessly upon the thick Turkey carpet. Almost opposite, across the open staircase, I could see into the large drawing-room, and there, to my amazement, I saw Kirk raising and lowering one of the blinds.

He was making the same signal to someone outside in the park as that made by the Professor before his death!