Green’s Dictionary of Slang

1. (later use Aus.) a warning shout that heralds an approaching master .

1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.
2001		OnLine Dict. of Playground Sl. 🌐 lobs v. call when teacher was coming, e.g. Keep lobs, stand lookout while others engage in fighting/burglary/sabotage etc.

2. a call for truce during a game.

1902		H. Baumann Londinismen (2nd edn).
1923		J. Manchon Le Slang.