Possible Clues:

• The Flushing Line is part of it: Abbr.
• NYC's original subway line
• Subway inits. still used by some very old Manhattanites
• Subway line to Columbia Univ
• N.Y.C. commuting debut of 1904
• The Bronx's Jerome Ave. line is part of it
• N.Y.C.'s first subway line
• NYC subway inits
• Old N.Y.C. subway inits
• Old N.Y.C. depot inits