I've seen one photo on twitter I think, where people parked trikes and cargo bikes in parking spaces filling a road and put on a comment, I'll just be a minute or similar, which I thought was good.The French equivalent of CTC hold a similar thing called 'Jusque deux minutes.' Or something similar. They park a few dozen bikes across a road, usually outside a Newsstand or similar and hold up the traffic and placards saying 'I'll just be two minutes.' Apparently in retaliation for motorists doing the same in cycle lanes. Much more effective IMHO.