They tried that here too
A woman in berkeley is struck in a crosswalk while using 'pedestrian flags'. They tried the flag thing here in Cambridge a year or two ago. The idea is that you have a number of these bright orange flags at both sides of a crosswalk. There's a little bucket at each end for them to be stored in and when you cross the road you grab one.

I seem to remember the flags here disappeared in about two days. I'm sure someone just swiped them. At this point there's no sign they even tried it.

One of the more interesting crosswalk things I've seen is one with a motion detector set up at either side of the road. The crosswalk is between blocks, and in an area with a number of elderly people. If someone is standing there waiting to cross the street, it senses it and a 'caution, person is crossing the road' sign lights up. There are also lights set into the pavement along the edges of the crosswalk (I'm wondering how those will last through the snow and a few plows). It seems to work pretty well, though it gets a number of false positives. This seems to be a much better solution to me because the flashing lights at least make someone driving along the road more aware that someone might be stepping out in front of them. And you don't have to worry about someone walking off with your flags.