If they're anything like the ones in Korea, they hire someone to be there during busy times, and whenever someone wants to cross, the person steps out with the flag and stops traffic. Usually in school zones.
You just pick one up and carry it across the road and then drop it off in the little bin on the other side. The idea is that you're more visible when you're holding a flag.
Amazing how America has to have the threat of damage to property to get people to not run over pedestrians, while Japan just has a little flag to increase visibility.
Hahahaha I think this sign is tongue in cheek. Most of the surrounding area outside of Granville Island is very easy to walk and enjoy yourself without a car. At Granville you have to be careful of a large influx of tourists in cars and cement mixer trucks.