they're like pedestrian crosswalk buttons that are in the middle of the crosswalks and they put them on major streets (ones with a curb in the center). this way, the bicyclist doesn't have to wait for a car that wants to turn left to come up behind him to set off the pressure pad under the street (which is why this is only needed on major streets). in this area, I've only seen it once and that was at the intersection of two major streets because then you don't get a lot of unnecessary red lights.
they basically look like a 3 foot pole with a crosswalk button on it.