Green’s Dictionary of Slang

1. (US Und.) wise, in the know; thus be George, to understand.

1921		P. & T. Casey Gay-cat 301: Be George or hep — to be wise. ‘Hello, George,’ said when meeting a bo is tantamount to meaning, ‘I’m a bo, too’.
1931		Irwin Amer. Tramp and Und. Sl. 85: George. – To be in the know or aware of what is impending.
1955		H. Braddy ‘Narcotic Argot Along the Mexican Border’ in AS XXX:2 87: GEORGE, adj. Trustworthy.
1956		E. Hunter Second Ending 300: How clever, how George, these hopheads sure know how to put things, hey!

2. (US) acceptable, satisfactory.

1930		‘Dean Stiff’ Milk and Honey Route 208: Jake or George – The same as hunkydory.
1953		W. Brown Monkey On My Back (1954) 14: He was silent a few seconds, then he managed a lop-sided grin. ‘George.’ ‘What’s that mean?’ ‘The squares say okay.’.
1955		Mad mag. Aug.–Sept. 25: Was he ‘george’? ... to use a popular expression meaning was he OK?
1960		C. Cooper Jr Scene (1996) 151: Thanks, my man. That was real George.
1971		E.E. Landy Underground Dict. (1972).