The North American Vexillological Association (NAVA) held its annual meeting (NAVA 17) at the Hotel St, Moritz in New York City, October 14-16, 1983. A special flag for the occasion featured the blue and orange colors of New York, with an apple in the center for the “Big Apple” (New York City’s nickname). A “Y” at the center was meant to resemble a subway token.
 
   
Wikipedia: North American Vexillological Association   
The North American Vexillological Association (NAVA) is a membership organization devoted to vexillology, the scientific and scholarly study of flags. It was founded in 1967 by American vexillologist Whitney Smith (1940–2016), and others. Its membership of 600+ comprises flag scholars, enthusiasts, designers, collectors, conservators, educators, merchants, manufacturers, historians, and hobbyists.
 
Wikipedia: Flags of New York City
The flag of NAVA Meeting 17, hosted in New York City. NAVA meeting flags often incorporate elements to reflect the host city.
 
North American Vexillological Association (NAVA)
NAVA 17: New York City, New York
Hotel St. Moritz
October 14–16, 1983
Details and additional photos of NAVA 17: NAVA News vol. 16, no. 6 (1983)
 
The NAVA 17 Flag:  Phil Allen’s design features New York City´s colors (blue, orange, and white) and an apple representing the city’s nickname, “The Big Apple”.  Within the apple is hidden the number 17 reminiscent of the cutout tokens used by the New York City Transit Authority in the mid-20th Century.
 
Meeting flag description from Flag Research Quarterly 11: The Flags of NAVA