Signallers were used from the 1800s and utilised flags to communicate with train drivers and various technologies over the years to communicate with signallers in other signal boxes.
Local signallers (controlling a small local area of train operations) are becoming rare; they work out of a signal box (sometimes called a signal cabin or interlocking tower).
Modern signalling systems usually have centralised traffic control centres, where a small number of signallers can control an entire rail network.
The main duty of the signaller is to maximise train movements in their designated area of operation.