Adelaide uses a feather style of signaling based on the British system.
This signal has the feather illuminated, indicating that we are going to turn out. There are also shunt lights under the main lights on this pole.
The signal prior to a turnout is generally flashing yellow, alerting the driver of the turnout so the train can be slowed. Turnouts can be shown with any colour, however it is rare to see a red signal with turnout unless there is an active shunt signal.
Adelaide also has AWS - Automatic Warning System. The yellow devices shown above transmit the state of the next signal with magnetic and electro-magnetic fields. The train's brakes can be applied if the driver does not acknowledge the signals.
For photos of the suburban control center, visit David Johonson's page.
More information is available about the British feather signalling systems, AWS and TPWS (more advanced AWS used for critical junctions). Just use a good search engine.