A device or control used to remind the SignallerA person responsible for the operation of the Signalling System, to safely control the passage and regulation of trains, usually located in a Signal Box. that a function such as a
button, switch or lever should not be operated/should only be operated
under certain conditions. See also CollarA facility that prevents the Signaller from operating an item of signalling infrastructure. Either a physical item preventing the pulling of a lever or operatio....