Pretty much every serious attempt at protecting pedestrians requires building refuges (which already exists) and devising ways to get drivers to actually slow down (as opposed to slapping a lower speed limit sign and hoping they'll do so). If you want to truly dissuade pedestrians from crossing, you need to erect a median barrier.

Merely putting up a sign sounds a lot more like the traffic department dealing with drivers' complaints of annoying jaywalkers in the least effort way possible.