Monticello Raceway (in Monticello, New York) has been called the “Mighty M” since 1960. “Mighty M” was printed in the Scranton (PA) Tribune on June 17, 1960.
   
Aqueduct Racetrack has been called the “Big A” since the late 1950s.
     
     
Wikipedia: Monticello Raceway
Monticello Gaming and Raceway is a harness racing track and racino in Monticello, Sullivan County, New York. It is off Exit 104 of Route 17 (future Interstate 86), on New York State Route 17B.
 
The racetrack is nicknamed “The Mighty M” and races standardbred horse races during the afternoons year-round. The current racetrack is a 1/2 mile oval. The track opened on June 27, 1958 in order to attract more people to Monticello’s resort area.
     
Newspapers.com
17 June 1960, Scranton (PA) Tribune, pg. 21, col. 1:
‘Mighty M’ Lures
Record 6,347 for
1960 Inaugural
By CHIC FELDMAN
Tribune Sports Editor
MONTICELLO, N. Y.—Everything from favored Tar Boy in the $5,000 feature “Sixty Special Pace” went according to form at the Mighty M Thursday night as MOnticello Raceway launched its third and scheduled most prosperous season with a 6,347 house which deposited $274,135 at the pari-mutuel windows.
 
18 June 1961, New York (NY) Times, “Monticello Reaps Seminar Harvest,” pg. S5, col. 6:
MONTICELLO, N. Y., June 17—Monticello Raceway’s school for neophyte bettors is paying off handsomely.
 
Franklin B. Devlin, the Mighty M’s president and general manager, recently instituted seminars in horse-playing at the hotels that abound in this Sullivan County resort area.
 
25 July 1961, New York (NY) Times, “Monticello Raceway Continues Steady Growth: Handle Expected to Reach $30,000,000” by Michael Strauss, pg. 22, col. 6:
MONTICELLO, N. Y., July 24—When officials at Monticello Raceway dubbed their cozy Catskill Mountain plant “The Mighty M” at the start of last year, there was considerable snickering. The picturesque half-mile oval, it was felt, did not rate such impressive billing.
   
Twitter
P.C.
@pickledcotton
Monticello Raceway: the Mighty M!
12:09 PM · Nov 26, 2009·Twitter Web Client
   
Twitter
DRF Harness
@DRFHarness
The Mighty M is back!
@HarnessEyeGuy on Monticello Raceway handle surge & other tracks. http://drf.com/news/giwner-monticello-has-been-mighty-handle
@USTrotting @HarnessRacingFZ
4:55 PM · Feb 4, 2015·Twitter Web Client
 
Best US Casinos
Monticello Gaming and Raceway in Sullivan County Will Impress You
By Jeremiah Booker
January 13, 2021
Monticello Gaming and Raceway is one of the premier harness racing destinations in Southeast New York. Located off Exit 104 on New York State Route 17B, the track has garnered the nickname “Mighty M,” and it currently hosts standardbred races all year round on its half-mile oval.