OS

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OS"On (train) sheet; to report a train by to dispatcher
OUT"When a trainman is at a point other than his home terminal, either on or off duty, he is out
OUTLAWED"See dogcatchers ...

OS
Means "entered on the sheet." Often used as a verb to report that a train has passed the tower.
Paddle ...

After the train had passed, the operator cleared the train-order signal, logged the train on his sheet, and contacted the DS: "OS Glenwood".

OS - Means "entered on sheet, " often used as a verb to indicate the reporting of a train which has passed a tower.
Overhead - Catenary and contact wire of an overhead electrical distribution system.

See also: Track, Train, Switch, Current, Class