In China, to stand on a bicycle is an announcement that you are about to speak publicly -- a risky thing to do there. It is equivalent to the American concept of standing on a soapbox -- although I have never actually seen anyone do this outside of Bughouse Square in Chicago. The reasoning is the same: to rise up and be seen by the crowd.

I know of an American who lost a friend in the crowd milling around Tiananmen Square in Beijing; despite being taller than most Chinese, he wanted a better vantage point from which to look around. So, he stood on his bicycle, and was immediately arrested. (Fortunately, he was able to convince the Gong An that he had no political intentions.)