when I first moved to Seattle, only a few intersections had sensors for bikes to trigger light changes. Often I'd have to waddle over to a crosswalk and press the pedestrian crossing button, or just wait for a car to come up behind me. Then I started noticing these little "T" shaped markings all over the place. I have no idea if I just didn't notice them at first or if they were installed in the last few years. 

The key is to get your tire over the "T". If your tire is merely near the " T" the light will not change in your favor.  

Some markings are big, some are small, but I see them at nearly every intersection with lights affected by sensors.  

What surprises me is how many cyclists I pedal up to who don't use the sensors. Even a Cascade Bicycle ride leader didn't know about the "T". They either sit, waiting for the light to turn on it's own, or hobble over to the pedestrian crosswalk. I've heard some cyclists think they could be anywhere over the car sensor to trigger it and I've heard some say they were too light (I'm pretty sure it's a magnet, people, not a scale) or that their bike was such a fancy compost that the magnet didn't respond. I am fully convinced it's all about having your tire RIGHT over the "T" as pictured in the photos. 

I, for one, am thanksgiving thankful for these sensors. My commute is better since their installation. Thank you, Seattle!