Green’s Dictionary of Slang

1. to plan, to scheme; to know something in advance.

c.1921		T. Norman Penny Showman 54: I was informed later that it was a put up job, and that it had all been ready eyed.
1981		(con. 1900–30) A. Harding in Samuel East End Und. 283: Ready eye – To plan.

2. to conduct a surveillance.

1981		(con. c.1920) A. Harding in Samuel East End Und. 185: Harry Boy Sabini came over and I ‘ready-eyed’ him.
2000		J.J. Connolly Layer Cake 7: They can’t get out the front door to put on a bet without the Robbery Squad ready-eying them there and back.