a high percentage of protesters involved would have to have a sign or banner to make it effective, but it would spread the police over a far greater area and you'd cover so much more ground... people would walk entire block lengths along the picket.
as long as it kept moving on the sidewalk it would be left alone.
also, the meeting area announced could cover a significantly larger part of town... instead of being at terry shrunk plaza, or pioneer square, the announced meeting area could cover 10 square blocks. people would converge from all directions making it impossible to pin down.
as with most of our tactical planning, this idea is now known to police and protesters alike. i would love a lower profile forum for strategy or info about regular planning meetings that take place in the 3D.