Green’s Dictionary of Slang

1. (US) $5, thus two-pound note $10 [the contemporary exchange rate of $5 = £1].

1931		D. Runyon ‘A Nice Price’ in Runyon on Broadway (1954) 191: Old Liverlips weakens and goes for a pound note.
1941		N. Davis ‘Don’t Give Your Right Name’ in Goulart (1967) 20: They [...] laid down a pound note to get in.
1951		R. Starnes Grant’s Tomb 115: I handed him [i.e. a cab-driver] a two pound note.
1952		(con. 1920s) ‘Harry Grey’ Hoods (1953) 291: I gave the elevator kid a pound note.

2. an upper-class person [i.e. rich].

1937		J. Curtis There Ain’t No Justice 51: Getting too good for us, are you, Miss Poundnote?
1958		F. Norman in Encounter Nov. in Norman’s London (1969) 54: This house it is full of a load of nut-cases [...] and quite a lot of them are right pound notes.
1962		F. Norman Guntz 15: I was working up West in the height of society and became a bit of a pound note myself.

3. any sum of money.

1954

Mad mag. Dec. 17: I want to be where the cash is ... the green stuff .... moolah .... pound notes .... get it ...? ...Money!