Green’s Dictionary of Slang

(UK und.) to keep a lookout.

1873

Illus. Police News 9 Aug. 4/3: [O]ne of them said that they intended give him a ‘domino’ (a slang term used by thieves, meaning to knock a man down and rob him), and they asked him to ‘Philip’ for them (that is, look out for the police while the robbery was being committed).