The City of Portland has been working with Portland State University students to determine whether the detection of bicycles at traffic signals can be best done with inductive loop detection or some other type. We have studied a variety of different detection types including video and microwave and thermal imaging and there are good applications for these different types depending on the infrastructure at your particular location.
The standard detection remains inductive loops and with that sort of equipment, it is important to get people on bikes in the right spot so the traffic signal infrastructure can work as designed. My experience in Boston, MA showed a new way of marking and signing where a person should locate themselves and their bike to get a green indication. I couldn't really determine what the sign meant. It's not intuitive to me and I wasn't sure where I was supposed to place my bicycle. I am hopeful someone will be able to tell me via the blog comments, without seeing the loop cuts in the pavement (see the last picture), I didn't know what the wording of the sign meant for me to do.
I would compare this sign to the following video on being detected using the standard sign and detector marking.