You can't fight the greater demon of war unless you start solving interpersonal problems even unto household and community disputes. The same chaos and strife you experience in these areas is only expanded into the larger social and political circles that few fully understand.
How can we even kid ourselves to attempt to bring peace with picket signs when we can't solve simple, small-circle misunderstandings?
Hug your children, volunteer at a soup kitchen, join a walk-for-donations campaign, call your congressman, donate to local non-profits. These things all directly relate to social improvement. Sitting all day with a sign does nothing to change anyones minds or actions.
I may even go so far as to say picketers in this sense are delusional and even subtract from the social-improvement of others. As we've identified picketers for peace are generally not aiding the problem of war, then they are wasting resources. Even the occupancy of the street corner can interfere with normal (possibly value adding) actions of those passing by.
It's one thing to picket for fair wages or something with a clear-cut solution. It's entirely another to try to deal with geo-political arguments through decorating signs.
Ambiguous signs that just say "peace now" or "no war" are the worst. There will be always be war.