Originally Posted by wonkypedantry

Zs1 Ersatzsignal

Zs1
Ersatzsignal = Subsidiary signal

Three white lights aligned as a triangle (pointing upwards), or one flashing white light.

Meaning: the train may pass the accompanying main signal (that shows 'halt' or no valid aspect) with a maximum speed of 40 km/h. Details: If there is a dark distant signal at the same place, at most this speed has to be used until the aspect of the following main signal is visible, and until that, it must be expected that the latter signal commands "halt". If the main signal is a (train station's) exit signal ("Ausfahrsignal"), this speed limit applies until the last set of points/switch has been passed by the complete train, after which regular speed is permitted. In case of entry and intermediate main signals of a train station ("Einfahrsignal"/"Zwischensignal"), the speed limit has to be obeyed until after the next main signal or up to the usual stopping location ("gewöhnlicher Halteplatz"). If several cases apply, the lowest speed given by any of them has to be followed.[5]

This signal may be used when a main signal fails or cannot be set to a proceed aspect (because preconditions are not met). One possibility is that one or more bulbs don't work, and the necessary aspect cannot be shown. For example, a signal which should show Hp2 (green + yellow, proceed with 40 km/h) could have a broken yellow bulb. It would therefore show Hp1 (green, proceed with maximum speed). This would be dangerous because it implies to the driver that he could run faster than is safe, so the signal must show stop instead. Another possibility is that one of the 'proving' devices (devices for proving that a section of line is safe - e.g. that a set of points/switch has moved completely). In this case, the section of track or set of points/switch affected must be checked manually to ensure that everything is safe for the passage of trains, and the signal Zs 1 would be given.[5]