It's actually even worse. The SHP don't even know the state of the signal at all. The only thing the system does is checking so that the driver has acknowledged that there actually is a signal. A few hundred meters before the main signal, there is a magnet on the right side of the track. When the train passes over it, the SHP lights shows up in the cab. As long as the driver resets it, nothing more will happen. Even if the signal is red.