A friend of mine has a son who is an engineer here in the Midwest, I asked him your questions, here is his response:

Had to do a little digging myself to answer that one and I am still uncertain if this is correct. The trains that operate over this route use something called pulse code cab signaling. Trains equipped with cab signaling have a display that constantly reminds the engineer what signal they are on to adjust the speed. Whats unique about Northeast Corridor trains is the speed they travel, being the only high speed rail in the country. There is a shoe that detects the frequency and will display a signal indication in the cab depending on what it reads, if I am understanding it correctly.

http://en.m.wikipedia.org/wiki/Pulse_code_cab_signaling