The city of Seattle has been nice enough to paint a little "T" over the spot that is most likely to trigger a traffic light at many intersections. I've noticed that my wheels don't trigger the signal nearly as effectively as my bottom bracket; but then, I ride a fairly heavy steel touring bike. At intersections that don't seem to work with bicycles, I either treat it like a malfunctioning signal and run the light if traffic is sparse, or use the pedestrian signal.

But honestly, unless it's very late at night, there is enough car traffic in the city that I don't need to worry about tripping signals; there's usually a huge massive car or SUV around to do it for me.