Green’s Dictionary of Slang

mary warner n.

(orig. US drugs) marijuana.

1923		Wash. Post 17 June n.p.: The first raid under the new ordinance out lawing Marijuana, a Mexican smoking weed better known as ‘Mary Warner’ and said to be in reality the East Indian Hashish, was made by the police today.
1933		Newsweek 5 Aug. 26: Marihuana cigarettes, better known to users as ‘reefers’, ‘muggles’, or ‘Mary Warners’.
1940		‘Jargon of Marihuana Addicts’ in AS XV:3 Oct. 336/2: The drug, itself, is known as [...] Mary Wanner, Mary Warner, Merry Wonder.
1953		Anslinger & Tompkins Traffic In Narcotics 312: Mary Werner. Marihuana. Also a marihuana cigarette.
1959		J.E. Schmidt Narcotics Lingo and Lore.
1962		Standard-Speaker (Hazleton, PA) 3 Apr. 11/3: He could have asked for a joy weed, a merry wonder, or a reefer, and it would have meant the same — a marijuana cigaret.
1969		R.R. Lingeman Drugs from A to Z (1970).
1971		‘Hassan-i-Sabbah’ Leaves of Grass 1: Maria Juanita / Mary Warner / Miggles.
1974		C. Loken Come Monday Morning 145: Maybe we oughta switch to dope, Nick – they say that marywana ain’t half bad.
2001		ONDCP Street Terms 14: Mary Warner — Marijuana.

In compounds

mary warner smoke (n.) [smoke n. (2a)]

(US) a marijuana cigarette.

1922

Ogden Standard & Examiner (UT) 24 Dec. 4/12: In America these cigarettes are called either ‘flying cigarettes’ or ‘Mary Warner’ smokes.