What type of signalling is used on the Boston subway?

what type of signalling system is used on the boston subway system?

Traditional block style signals on the Green Line and Blue Line.

Computerized on the Red Line & Orange Line, like cab signals, except for interlockings, which have signals.

This page has a description of Green Line signal indications:

http://world.nycsubway.org/us/boston/green-subway.html