What is defined as a block or interlocking signal without a number plate?

An absolute signal is specifically defined as a block or interlocking signal that does not include a number plate. This characterization is important because absolute signals provide critical information to train crews regarding their authority to proceed within a given block or track segment. The absence of a number plate indicates that the signal's function is strictly to provide a binary indication—either stop or proceed—without the need for additional instructions that would typically be associated with signals displaying a number plate.

In railroad signaling, the distinction of an absolute signal is significant for operational safety. It informs train operators that they are either permitted to proceed (for example, if the signal shows a clear indication) or must stop (if the signal indicates halt). Understanding these signals is crucial for managing train movements safely and effectively within a rail network.

Other types of signals, like block signals, control signals, and proceed indications, serve different roles or might include additional information or context, but they do not fit the specific definition of what constitutes an absolute signal in terms of lacking a number plate.