I have definitely seen "parade route" signs taped to lampposts in advance in my city. Pretty sure that most large protests require permits and advance notice so

I have definitely seen "parade route" signs taped to lampposts in advance in my city. Pretty sure that most large protests require permits and advance notice so that extra police can be made available, traffic can be rerouted, the protest's own route and scope can be approved. Because otherwise every protest would outdo the next to take the most disruptive form possible, so as to get maximum publicity.