I assume they mean climb down from the cab and pick up the phone on the post to request permission with signals which was a thing in the past. Real world now uses the in cab radio - with the SIG or "Signal isn't green" button
If that's what they mean it woulf be a neat little feature, definetly with routes set in the past and random events, so you'd come up to a red signal, climb out, call the signaller who tells you to pass at restricted speed because the signal is faulty. You can then continue on your journey
