The recommendation cited reads " Would suggest propeller notice boards being permanently fitted on outside of ship's side rails in way of after Docking bridge, as is the practice in other Company's Steamers. Thus saving the placing & stowing away of these boards every voyage with corresponding destruction to the painting and printing."
From the position of the board in the photo, it wasn't carried out on Titanic. It's certainly not "in way of after docking bridge".
On page 116 of Olympic and Titanic: The Truth Behind the Conspiracy, there's an undated photo of Olympic showing a sign exactly where Andrews wanted it.