I don't think they are common in Tokyo. I've seen them few times, maybe. In most cases people just put their umrellas in an umbrella stands in front of the stores, restaurants or combini. Since most of them look similar, people get confused about which one is theirs. I've heard that nothing gets stolen in Japan, except for bikes and umbrellas. Not sure about bicycle - still got mine, but indeed I've got my unmbrella misplaced once or twice.