Which type of signal never shows a clear indication but always displays a red light?

The type of signal that never shows a clear indication but always displays a red light is a dwarf marker. Dwarf markers are typically used in areas where space restrictions prevent the installation of standard-sized signals. Their primary purpose is to convey a restrictive aspect, which means they signify "stop" or "proceed with caution," but they do not provide any clear proceeding signal such as green or yellow.

Because they remain at a constant red light, these signals are designed to ensure that train operators maintain a safe speed and stop as necessary, ensuring safety in scenarios where visibility may be compromised or where other signal types cannot be effectively utilized. In contrast, main signals, warning signals, and intermediate signals are intended to provide various indications depending on the operational context and train movements, thereby displaying a range of colors including clear indications for proceeding safely.