Manual block signaling systems use signals to communicate movement authority from the block operator to the train crew. These signals indicate whether a train may proceed into a block or must stop and wait for further authority.
One of the most common signal types used in early manual block systems was the semaphore signal. Semaphore signals use a movable arm to display different signal indications based on the arm position.
In most semaphore systems, a horizontal arm position indicates "Stop," meaning the train must not pass the signal. An angled downward position, commonly at 45 or 60 degrees, indicates "Clear" or "Proceed," allowing the train to enter the block.
Some manual block territories later used manually operated color light signals. These signals display colored lights controlled by the block operator to indicate movement authority.
In color light systems, a red light generally indicates "Stop," while a green light indicates "Clear" or "Proceed." Some systems may also use yellow or other colors for additional restricted indications depending on operating rules.
Train order signals may also be used in manual block territory. These signals inform train crews whether they must stop to receive train orders from the block operator or may continue without stopping.
Marker boards and fixed signals are sometimes installed to identify the physical boundaries of each block. These signs help train crews identify block limits during operation.
The meaning of signal indications is defined by railroad operating rules, and train crews must strictly obey all displayed signal indications to ensure safe train separation and operation.