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> And I believe this was a way to annotate that something was… fixed, maybe? Or on its way to being fixed?

A "Rotte" is the crew working on railway construction. So I assume this is a label to warn that personnel is on the tracks

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To add to this, those signalling panels (SpDr is the series, I think) work on the principle “from where to were”: you hold down the button for the signal that is showing red, then press the button for the track you want to direct the train to. The system then checks if that doesn’t cross an already-configured path of another train (if so, it refuses to do anything), then sets the relevant track switches as required and finally changes the light on the signal.

The marker is on one of the destination buttons to remind the signaller not to send any trains there, because that might endanger the people working there.

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