Green’s Dictionary of Slang

(US Und.) a large-denomination dollar bill, esp. when used to impress a confidence man’s potential victim.

1938		D. Runyon ‘Pick the Winner’ in Runyon on Broadway (1954) 319: Large coarse notes are so scarce in Miami.
1940		D. Maurer Big Con 94: The cashier always has a ready stack of ‘coarse ones’.